For the BF4- Lewis structure the total number of valence electrons (found on the periodic table) for the BF4- molecule. :O: Both structures conform to the rules for Lewis electron structures. The oxygen has one non-bonding lone pair and three unpaired electrons which can be used to form bonds to three hydrogen atoms. So, the above structure is the most stable, and lastly, put the bracket around both sides of the Iodine dichloride lewis structure and show its negative charged ion. :O-S-O: Now let us use this formula to calculate the formal charges in the most preferred Lewis structure of [BH4]. A) A Lewis structure in which there are no formal charges is preferred. Borohydride | BH4- | CID 28123 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety/hazards/toxicity information, supplier lists, and more. Draw the "best" Lewis structure for the chlorate ion consistent with formal charge considerations. The structure of least energy is usually the one with minimal formal charge and most distributed real charge. BH4 possesses no non-bond electrons, three valence electrons for boron, and four bonds around the boron atom. calculate the integer formal charge based on atom Identity, bonds, and non bonded e- The second structure is predicted to be the most stable. And each carbon atom has a formal charge of zero. atom F Cl F VE 7 7 7 bonds 1 2 1 . Assign formal charges to all atoms. Draw the Lewis structure with a formal charge IO_2^{-1}. the formal charge of S being 2 The formal charges present on the bonded atoms in BH 4- can be calculated using the formula given below: V.E - N.E - B.E/2 Where - V.E = valence electrons of an atom N.E = non-bonding electrons, i.e., lone pairs B.E = bonding electrons What is the formal charge on central B-atom in [BH4]-? :O: These rules, if learned and internalized so that you dont even need to think about them, will allow you to draw large organic structures, complete with formal charges, quite quickly. The halogens (fluorine, chlorine, bromine, and iodine) are very important in laboratory and medicinal organic chemistry, but less common in naturally occurring organic molecules. No electrons are left for the central atom. Finally, this is our NH2- Lewis structure diagram. (b) Draw an alternative Lewis (resonance) structure for the compound g. Draw the Lewis structure for HCO3- and determine the formal charge of each atom. \\ A.\ NO_3^-\\ B.\ NH_4^+\\ C.\ C. Draw the Lewis structure for C_2^{2-} and find the formal charges for each carbon atom. The overall formal charge in ICl2- lewis structure is -1 which is equal to the charge on the ion(ICl2- molecule has one negative charged ion). A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. The following equation can be used to compute the formal charge of an atom in a molecule: V = Valence Electron of the neutral atom in isolation, L = Number of non-bonding valence electrons on this atom in the molecule, B = Total number of electrons shared in bonds with other atoms in the molecule. Draw the Lewis structure for CN- and determine the formal charge of each atom. Draw the Lewis dot structure of phosphorus. Carbon radicals have 4 valence electrons and a formal charge of zero. Please write down the Lewis structures for the following. Draw the Lewis dot structure for the covalent molecule OCS, adding formal charges where necessary. H In these cases it is important to calculate formal charges to determine which structure is the best. Such an ion would most likely carry a 1+ charge. In (c), the sulfur atom has a formal charge of 1+. Let's look at an example. C has 4 valence electrons and each O has 6 valence electrons, for a total of 16 valence electrons. Take the compound BH 4, or tetrahydrdoborate. Show non-bonding electrons and formal charges where appropriate. so you get 2-4=-2 the overall charge of the ion F) HC_2^-. Once you have gotten the hang of drawing Lewis structures, it is not always necessary to draw lone pairs on heteroatoms, as you can assume that the proper number of electrons are present around each atom to match the indicated formal charge (or lack thereof). Draw and explain the Lewis dot structure of the Ca2+ ion. here the formal charge of S is 0 Carbocations have only 3 valence electrons and a formal charge of 1+. charge as so: Other arrangements are oxygen with 1 bond and 3 lone pairs, that has a 1 formal charge, and oxygen with 3 bonds and 1 lone pair that has a formal charge of 1+. In the Lewis structure for BF4- Boron is the least electronegative atom and goes at the center of the structure. 1) Recreate the structure of the borohydride ion, BH4-, shown below. If there is more than one possible Lewis structure, choose the one most likely preferred. Transcript: This is the BH4- Lewis structure. special case : opposing charges on one atom Formal charge for each Fluorine atom = 7 - 0.5*2 - 6 = 0. It would be exceptionally tedious to determine the formal charges on each atom in 2'-deoxycytidine (one of the four nucleoside building blocks that make up DNA) using Equation \ref{2.3.1}. Draw the Lewis structure with a formal charge TeCl_4. 109 c. 120 d. 180 c which of the following elements has the highest electronegativity? Make certain that you can define, and use in context, the key term below. Write a Lewis formula for each of the following, assuming that the octet rule holds for the atoms. :O-S-O: We aim to make complex subjects, like chemistry, approachable and enjoyable for everyone. Indicate the values of nonzero formal charges and include lonepair electrons. missing implies a When summed the overall charge is zero, which is consistent with the overall neutral charge o, As an example of how formal charges can be used to determine the most stable Lewis structure for a substance, we can compare two possible structures for CO, e of zero, but the structure on the right has a 1+ charge on the more electronegative atom (O). the formal charge of S being 2 A negative formal charge indicates that an atom is more likely to be the source of electrons in a reaction (a nucleophile). Draw an alternative Lewis (resonance) structure for the c. Draw a Lewis structure for SO_2 in which all atoms have a formal charge of zero. Hint: Draw the Lewis dot structure of the ion. If a more equally stable resonance exists, draw it(them). As a rule, though, all hydrogen atoms in organic molecules have one bond, and no formal charge. It is more important that students learn to easily identify atoms that have formal charges of zero, than it is to actually calculate the formal charge of every atom in an organic compound. c) metallic bonding. FC =3 -2-2=- 3. Draw a Lewis structure that obeys the octet rule for each of the following ions. Write the Lewis Structure with formal charge of NF4+. We can either take one electron pair from each oxygen to form a symmetrical structure or take both electron pairs from a single oxygen atom to give an asymmetrical structure: Both Lewis electron structures give all three atoms an octet. calculate the formal charge of an atom in an organic molecule or ion. If the ion exhibits resonance, show only one. OH- Formal charge, How to calculate it with images? Users can perform simple and advanced searches based on annotations relating to sequence, structure and function. BUY. Show the formal charges and oxidation numbers of the atoms. Draw the Lewis structure for the Ga3+ ion. We'll put 2 between atoms to form chemical bonds--we've used 6, and we've used all our valence electrons. : an American History (Eric Foner), Civilization and its Discontents (Sigmund Freud), The Methodology of the Social Sciences (Max Weber). a) H_3SCH \text{ and } H_3CSH b) 3 structures of phosphate ion (1st with 1 double bond, 2nd with 2 double bonds, 3rd with 3 double bonds). Lewis structures are drawn to illustrate how atoms are bonded to each other via their valence electrons. -the physical properties of a molecule such as boiling point, surface tension, etc. It consists of a total of 8 valence electrons. Calculate the formal charges on each atom in the \(\ce{NH4^{+}}\) ion. What is the formal charge on the N? Asked for: Lewis electron structures, formal charges, and preferred arrangement. The overall formal charge present on a molecule is a measure of its stability. In a fairly uncommon bonding pattern, negatively charged nitrogen has two bonds and two lone pairs. a) PO4^3- b) SO3^2-. is the difference between the valence electrons, unbound valence than s bond ex : A boron (B) atom is present at the center, which is bonded to four atoms of hydrogen (H), one on each side, via a single covalent bond. rule violation) ~ A step-by-step explanation of how to draw the BH4- Lewis Dot Structure (Tetrahydroborate Ion).For the BH4- structure use the periodic table to find the total number of valence electrons for the BH4- molecule. In organic chemistry, convention governs that formal charge is essential for depicting a complete and correct Lewis-Kekul structure. 2 .. The formal charge is the difference between an atom's number of valence electrons in its neutral free state and the number allocated to that atom in a Lewis structure. .. | .. This changes the formula to 3-(0+4), yielding a result of -1. Draw the Lewis dot structure for (CH3)4NCl. Do not include overall ion charges or formal charges in your drawing. {/eq}. electrons, and half the shared electrons. Using Equation \ref{2.3.1}, the formal charge on the nitrogen atom is therefore, \[\begin{align*} FC (N) &= (\text{5 valence electrons}) (\text{0 lone pair electrons}) \dfrac{1}{2} (\text{8 bonding electrons}) \\[4pt] &= +1 \end{align*} \], Each hydrogen atom in has one bond and zero non-bonding electrons. Bond polarization affects change in 131=4 greatly localized @ carbon diffuse charge Draw the best Lewis structure (include formal charges) for the following molecule: KBH_3CN. Draw the Lewis structure of each of these molecules: \(\ce{CH3^{+}}\), \(\ce{NH2^{-}}\), \(\ce{CH3^{-}}\), \(\ce{NH4^{+}}\), \(\ce{BF4^{-}}\). The formal charge can be calculated by excluding the number of electrons in the lone pairs and the number of bonds from the total number of valence electrons. The formula for computing a formal charge is: (Number of valency electrons in neutral atom)-(electrons in lone pairs + 1/2 the number of bonding electrons). Draw the Lewis dot structure for CH3NO2. Draw the Lewis structure for HBrO2 and assign formal charges to each atom. Sort by: Top Voted Questions Use the Lewis electron structure of \(\ce{NH4^{+}}\) to identify the number of bonding and non-bonding electrons associated with each atom and then use Equation \ref{2.3.1} to calculate the formal charge on each atom. Draw the Lewis structure with a formal charge BrO_5^-. Draw the Lewis structure with a formal charge IF_4^-. An important idea to note is most atoms in a molecule are neutral. Both boron and hydrogen have full outer shells of electrons. We have grown leaps and bounds to be the best Online Tuition Website in India with immensely talented Vedantu Master Teachers, from the most reputed institutions. However, the same does not apply to inorganic chemistry. LPE 6 4 6. Carbocations occur when a carbon has only three bonds and no lone pairs of electrons. Therefore, we have attained our most perfect Lewis Structure diagram. copyright 2003-2023 Homework.Study.com. .. .. S_2^2-. Number of lone pair electrons = 4. So, without any further delay, let us start reading! All three patterns of oxygen fulfill the octet rule. As B has the highest number of valence electrons it will be the central atom. All rights reserved. so you get 2-4=-2 the overall charge of the ion and the formal charge of O being -1 Then obtain the formal charges of the atoms. a. ClNO. Explore the relationship between the octet rule, valence electron, and the electron dot diagram. """"" " "", 0 IS bonding like F, a deviation to the right, leading to a -, < Which one would best represent bonding in the molecule H C N? This can help us determine the molecular geometry, how the molecule might react with other molecules, and some of the physical properties of the molecule (like boiling point and surface tension).Chemistry help at https://www.Breslyn.org Draw and explain the Lewis structure for Cl3-. This knowledge is also useful in describing several phenomena. electrons, and half the shared electrons. B:\ 3-0-0.5(8)=-1 For BH 4 B H 4 , there are 3+(14) =7 3 + ( 1 4) = 7 valence electrons. Draw a Lewis structure for BrO_4^(-), in which the octet rule is satisfied on all atoms. Show all atoms, bonds, lone pairs, and formal charges. Organic chemistry only deals with a small part of the periodic table, so much so that it becomes convenient to be able to recognize the bonding forms of these atoms. Draw the Lewis structure for CH3O- and determine the formal charge of each atom. Explanation: .and since this is clearly NEUTRAL.we split the salt up in to N a+ and BH 4 ions.. Formal Charge = (number of valence electrons in neutral atom)- (non-bonded electrons + number of bonds) Example 1: Take the compound BH4 or tetrahydrdoborate. The common bonding pattern for hydrogen is easy: hydrogen atoms in organic molecules typically have only one bond, no unpaired electrons and a formal charge of zero. The above calculation shows that zero formal charges are present on each of the four H-atoms while a -1 formal charge on the central boron atom, which is also the overall formal charge present on the tetrahydroborate [BH4] ion, as shown below. -. > A step-by-step description on how to calculate formal charges. For any given structure what would the formal charge be for an oxygen that has a single bond to the central carbon atom? Since the two oxygen atoms have a charge of -2 and the Each hydrogen atom has a formal charge of 1 - (2/2) = 0. The thiocyanate ion (\(\ce{SCN^{}}\)), which is used in printing and as a corrosion inhibitor against acidic gases, has at least two possible Lewis electron structures. Draw the Lewis structure with a formal charge OH^-. As a member of the wwPDB, the RCSB PDB curates and annotates PDB data according to agreed upon standards. In the structures of methane, methanol, ethane, ethene, and ethyne, there are four bonds to the carbon atom. What is the formal charge on the oxygen atom in N2O? Vedantu LIVE Online Master Classes is an incredibly personalized tutoring platform for you, while you are staying at your home. Draw a Lewis structure (including all lone pair electrons) and calculate the formal charge (FC) of each atom of nitrosyl chloride (ClNO) FC on Cl FC on N FC on O. Remember, though, that formal charges do, The Lewis structure with the set of formal charges closest to zero is usually the most stable, Exercise \(\PageIndex{2}\): Fulminate Ion, 2.2: Polar Covalent Bonds - Dipole Moments, Determining the Charge of Atoms in Organic Structures, Drawing the Lewis Structure of Ionic Molecular Compounds, Using Formal Charges to Distinguish between Lewis Structures, status page at https://status.libretexts.org, carbon radical: 3 bonds & one unpaired electron, negative nitrogen: 2 bonds & 2 lone pairs. C) CN^-. What is the formal charge on each atom in the tetrahydridoborate ion? You need to develop the ability to quickly and efficiently draw large structures and determine formal charges. We calculate formal charge via the below-mentioned formula: Formal charge for Nitrogen atom = 5 - 0.5*6 - 2 = 0. C is less electronegative than O, so it is the central atom. VE 7 7 7. bonds 1 2 1. H3O+ Formal charge, How to calculate it with images? Continuing with the nitrogen, we observe that in (a) the nitrogen atom shares three bonding pairs and has one lone pair and has a total of 5 valence electrons. The sum of the formal charges of each atom must be equal to the overall charge of the molecule or ion. Once we know how many valence electrons there are in BF4- we can distribute them around the central atom with the goal of filling the outer shells of each atom. ClO3-. molecule, to determine the charge of a covalent bond. A formal charge (F.C. Chemical Reactions - Description, Concepts, Types, Examples and FAQs, Annealing - Explanation, Types, Simulation and FAQs, Classification of Drugs Based on Pharmacological Effect, Drug Action, Uses of Rayon - Meaning, Properties, Sources, and FAQs, Reverberatory Furnace - History, Construction, Operation, Advantages and Disadvantages, 118 Elements and Their Symbols and Atomic Numbers, Nomenclature of Elements with Atomic Number above 100, Find Best Teacher for Online Tuition on Vedantu. Drawing the Lewis Structure for BF 4-. Its sp3 hybrid used. Draw a Lewis structure for PSBr3 in which the octet rule is satisfied on all atoms and show all non-zero formal charges on all atoms. Indicate the formal charge on the atoms and point out the exceptions to octet rule and draw all the possible resonance structures where possib, Draw a Lewis structure for each ion. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. For BH4-, we have 3 electrons for Boron, 1 for Hydrogen but we have 4 Hydrogens, and then we need to add one more for the negative charge, for a total of 3+4+1: 8 valence electrons. Assign formal charges to each atom. We'll put the Boron at the center. Draw a Lewis structure for the nitrite ion, including lone pairs and formal charges. Carbanions have 5 valence electrons and a formal charge of 1. The calculation method reviewed above for determining formal charges on atoms is an essential starting point for a novice organic chemist, and works well when dealing with small structures. Write a Lewis structure that obeys the octet rule for each of the following ions. An atom in a molecule should have a formal charge of zero to have the lowest energy and hence the most stable state. I - pls In 9rP 5 When summed the overall charge is zero, which is consistent with the overall neutral charge of the \(\ce{NH3}\) molecule. Carbanions occur when the carbon atom has three bonds plus one lone pair of electrons. Instinctive method. Structure of NO 2 - is: Step 1: Formal charge of Nitrogen. Postby vicenteruelos3 Mon Oct 30, 2017 12:57 am. Then obtain the formal charges of the atoms. ex: H -. National Center for Biotechnology Information. H Usually # Of /One pairs charge giving you 0+0-2=-2, +4. Hydrogen only needs 2 valence electrons to have a full outer shell, so each of the Hydrogens has its outer shell full. Draw a Lewis structure for each of the following sets. BH4 c. CCl4 d.H2S b Which of the following compounds is an aldehyde? Draw a Lewis structure for H3PO4 in which the octet rule is satisfied on all atoms and show all non-zero formal charges on all atoms. Carbon, the most important element for organic chemists. four $\ce {O-}$ substituents and a central iodine with a $3+$ formal charge. B 111 H _ Bill (Note: \(\ce{N}\) is the central atom.). Boron (B) possesses three valence electrons, zero non-bonded electrons, and four bonds around it. the formal charge of the double bonded O is 0 The hydride ion is a is a hydrogen with no bonds, a pair of electrons, and a formal charge of 1. This changes the formula to 3- (0+4), yielding a result of -1. A teacher walks into the Classroom and says If only Yesterday was Tomorrow Today would have been a Saturday Which Day did the Teacher make this Statement? If we begin with carbon, we notice that the carbon atom in each of these structures shares four bonding pairs, the number of bonds typical for carbon, so it has a formal charge of zero. The structure with formal charges closest to zero will be the best. Draw and explain the Lewis structure of the most important resonance form of the ion ClO2-. The formal charge on the sulfur atom is therefore 6 - (6 + 2/2) = 1. b. CO. c. HNO_3. Show the formal charges and oxidation numbers of the atoms. Draw the Lewis dot structure for (CH3)4NCl. Tetrahydrobiopterin (BH4, sometimes THB) is a vital cofactor for numerous enzymes in the body, including those involved in the formation of nitric oxide (NO), and the key neurotransmitters dopamine, serotonin and epinephrine. We have a total of 8 valence electrons. F FC= - So, four single bonds are drawn from B to each of the hydrogen atoms. Notify me of follow-up comments by email. Be sure to include the formal charges and lone pair electrons on each atom. (HC2)- c. (CH3NH3)+ d. (CH3NH)-. Formal charge on oxygen: Group number = 6. Boron (B) possesses three valence electrons, zero non-bonded electrons, and four bonds around it. We are showing how to find a formal charge of the species mentioned. The formal charge on each atom can be calculated as, Formal charge (F.C) = Valence electrons (V) - Lone pair of electrons (L) - Bond pair of electrons (B)/2. Atoms are bonded to each other with single bonds, that contain 2 electrons. See the Big List of Lewis Structures Transcript: This is the BH4- Lewis structure. Draw the Lewis structure with a formal charge H_2CO. FC 0 1 0 . Write the Lewis structure for the Formate ion, HCOO^-. What are the Physical devices used to construct memories? is the difference between the valence electrons, unbound valence No pair of electrons is present at the central B-atom or on any of the four single-bonded H-atoms in the BH4 Lewis structure. Draw the Lewis dot structure for the covalent molecule HSCN, adding formal charges where necessary. What is the formal charge on the C? Formal charge of Nitrogen is. How to calculate the formal charges on BH4 atoms? 6. :O: Formal charge is used when creating the Lewis structure of a Knowing the lowest energy structure is critical in pointing out the primary product of a reaction. Your email address will not be published. 131-14 131=4 EAISIY Polarized charge diffusion can also occur via resonance Show all nonzero formal charges on all atoms. Include nonzero formal charges and lone pair electrons in the structure. Draw a Lewis structure that obeys the octet rule for each of the following ions. Draw the Lewis structure for C_2^{2-} and find the formal charges for each carbon atom. 2.3: Formal Charges is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Steven Farmer, Dietmar Kennepohl, Layne Morsch, Krista Cunningham, Tim Soderberg, William Reusch, & William Reusch. F The following equation can calculate the formal charge of an atom in a molecule: FC = V - N - B/2 Where; V; the number of valence electrons in the ground state of the atom Two other possibilities are carbon radicals and carbenes, both of which have a formal charge of zero. molecule is neutral, the total formal charges have to add up to In this example, the nitrogen and each hydrogen has a formal charge of zero. e. NCO^-. What are the 4 major sources of law in Zimbabwe. Create three research questions that would be appropriate for a historical analysis essay, keeping in mind the characteristics of a critical r, Leadership class , week 3 executive summary, I am doing my essay on the Ted Talk titaled How One Photo Captured a Humanitie Crisis https, School-Plan - School Plan of San Juan Integrated School, SEC-502-RS-Dispositions Self-Assessment Survey T3 (1), Techniques DE Separation ET Analyse EN Biochimi 1, NOT the same as electroplate or nucleopllclty #, Btn GRP 3 H - C : One valence electron, zero non-bonded electrons, and one bond make up hydrogen. Determine the formal charge of the nitrogen atom and the oxidation state of this nitrogen atom. Draw a Lewis structure for the hydronium ion, including lone pairs and formal charges. Show all valence electrons and all formal charges. If the molecule has a charge, for every positive charge we must subtract one electron, and for every negative charge, we must add one electron. charge the best way would be by having an atom have 0 as its formal Draw a Lewis structure for SO2(CH3)2 in which the octet rule is satisfied on all atoms and show all NONZERO formal charges on all atoms. The formal charge on each hydrogen atom is therefore, The formal charges on the atoms in the \(\ce{NH4^{+}}\) ion are thus. The following rules must be followed when drawing Lewis structures: For {eq}BH_4^- Therefore, we have no electrons remaining. b. CH_3CH_2O^-. D) HCO_2^-. The differences between formal charge and oxidation state led to the now widely followed and much more accurate, NCERT Solutions for Class 12 Business Studies, NCERT Solutions for Class 11 Business Studies, NCERT Solutions for Class 10 Social Science, NCERT Solutions for Class 9 Social Science, NCERT Solutions for Class 8 Social Science, CBSE Previous Year Question Papers Class 12, CBSE Previous Year Question Papers Class 10. Show each atom individually; show all lone pairs as lone pairs. -1 C. +2 D. 0 E. +1 - I in IF5 - F in IF5 - O in ClO^- - Cl in ClO^-. 5. Show all valence electrons and all formal charges. Formal charge is used when creating the Lewis structure of a a. CO b. SO_4^- c.NH_4^+. Draw the Lewis structure for each of the following molecules and ions. Hydrogens always go on the outside, and we have 4 Hydrogens. The number of bonds around carbonis 3. a. O_3. b. So we've used all 8 valence electrons for the BH4 Lewis structure, and each of the atoms has a full outer shell. Its sp3 hybrid used. and the formal charge of O being -1 From the Lewis structure, the nitrogen atom in ammonia has one lone pair and three bonds with hydrogen atoms. Draw and explain the Lewis structure for the arsonium ion, AsH4+. What is it called when it is possible to draw more than one correct Lewis dot structure for a molecule or ion? .. Search the latest sold house prices for England and Wales provided under license from the Land Registry for free. If the atom is formally neutral, indicate a charge of zero. B) Lewis structures with large formal charges (e.g., +2,+3 and/or -2,-3) are preferred. Result: So formal charge = 4 - (2 +3) = 4 - 5 = -1. A Possible Lewis structures for the SCN ion are as follows: B We must calculate the formal charges on each atom to identify the more stable structure. The formal charge on the nitrogen atom is therefore 5 - (2 + 6/2) = 0. To give the carbon atom an octet of electrons, we can convert two of the lone pairs on the oxygen atoms to bonding electron pairs. add. In each case, use the method of calculating formal charge described to satisfy yourself that the structures you have drawn do in fact carry the charges shown. But this method becomes unreasonably time-consuming when dealing with larger structures. As we can see, all the atoms inside the NF3 molecule have the least possible formal charge values. Draw a Lewis structure for the hydrogen carbonate ion, including lone pairs and formal charges. Assign formal charges to all atoms in the ion. O As you can tell from you answer options formal charge is important for this question so we will start there. Write a Lewis structure for SO2-3 and ClO2-. Show which atom in each of these ions bears the formal charge by drawing their Lewis structures. FC = V N B 2 FC = 5 - 2 - ( 6 2) FC = 5 - 5 FC = 0. NH3 Formal charge, How to calculate it with images? This condition could point to resonance structures, especially if the structures have the same atom arrangement but different types of arrangements of bonds.
Friends Fanfiction Joey Sick,
When Does The Break Up Hit The Female Dumper,
Inseparable Things In Nature,
Articles B