chemistry-chap-4 – Flashcards

1. nonpolar covalent -If the electronegativity difference (usually called ?EN) is less than 0.5, then the bond is . 2. polar covalent-If the ?EN is between 0.5 and 1.6, the bond is considered 3.ionic- If the ?EN is greater than 2.0, then the bond is

NO

P4O10

CH4

When two bonded atoms attract electrons with equal strength,

one in which the electrons are unequally shared between the atoms.

results when the sharing is so unequal that fully charged ions form.

Iodine heptafluoride

When the molecule has just single bonds we use the -ane suffix.The simplest carbon molecules are compounds of just carbon and hydrogen, hydrocarbons. We name the compounds based on the length of the longest carbon chain. We then add prefixes and suffixes to describe the types of bonds and any add-ons the molecule has.

are compounds that have the same formula but different bonding.

When an alkane is a substituent group they are named using the -yl ending instead of the -ane ending. So, -CH3 would be a methyl group.

When a hydrocarbon has a double bond we replace the -ane ending with -ene

Hydrocarbons with triple bonds are named basically the same, we replace the -ane ending with -yne.

carbon tetrachloride

dinitrogen pentoxide

carbon forms 4 covalent bonds in neutral compounds Covalent bonding involves the sharing of electrons between atoms. The number of covalent bonds an atom can form relates to the number of electrons it can share and still result in a neutral molecule. It is important to know how many bonds certain elements will form in order to draw structural formulas for molecules.

oxygen forms 2 covalent bonds in neutral compounds (has 2 lone pairs) Covalent bonding involves the sharing of electrons between atoms. The number of covalent bonds an atom can form relates to the number of electrons it can share and still result in a neutral molecule. It is important to know how many bonds certain elements will form in order to draw structural formulas for molecules.

nitrogen forms 3 covalent bonds in neutral compounds (has 1 lone pair)

hydrogen forms 1 covalent bond in neutral compounds

For part A the answer is D because Oxygen has 6 valence electronsand can form up to 2 bonds.

Part B there should on be one electron for hydrogen, Hydrogen onlyhas one electron

answer is d Bromine has 7

8 and 8

the line indicates the bond between S and Cl and each line is two bonding electrons so there are 4 bonding electrons and the remaining are non bonding electrons So there are 16 non bonding electrons so the answer is 4,16

For the SiCl2Br2 Lewis structure, calculate the total number of valence electrons for the SiCl2Br2 molecule (SiCl2Br2 has 32 valence electrons). After determining how many valence electrons there are in SiCl2Br2, place them around the central atom to complete the octets.

CS2 and CO3-2 follow the octet rule.The octet rule is a chemical rule of thumb that reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. PF5 is an exception to the octet rule and will work.CO3-2 will satisfy the rule because it hastwo extra electrons which is why the compound has a -2 charge.CS2 simply follows the rule.Phosphorus pentachloride (PCl5) and sulfur hexafluoride (SF6) are examples of molecules that deviate from the octet rule by having more than 8 electrons around the central atom.

0 In neutral covalent compounds, boron typically has three bonds and no lone pairs. Therefore it has only six electrons around it (not eight), which is why it is an exception to the octet rule.

BrF3 should have 2 lone pairs (four unshared electrons total) on the central atom.In this compound, Br has a total of ten electrons around it (not eight), which is why it is an exception to the octet rule.

In this compound, Xe has a total of twelve electrons around it (not eight), which is why it is an exception to the octet rule. Hydrogen is also an exception because is it stable with only two electrons rather than eight.

How to: To calculate formal charge of an atom, use the equation below. Take the valence number of the atom and subtract the number of bonds and the number of non-bonding electrons.

Resonance increases rather than decreases stability. Think about the molecules knocking around against each other. A lone pair might be shifted from the oxygen toward the carbon, increasing the electron density on the second oxygen. The answer is O=C=O and O?C?O

There are two resonance structures for O3 (ozone). - Resonance structures are necessary to show how electrons are distributed in chemical bonds in a molecule. - Remember, the molecule isn't flipping back and forth between structures! It's an average of the resonance structures.

The Lewis structures in Figure 1 indicate that the ozone molecule has two equivalent resonance structures, which means the electrons are delocalized. From the Lewis structure, we see that the bond order for O2 is 2 (a double bond), whereas the bond order for O3 is 1.5 (one and a half bonds). Scientists previously believed that a molecule such as ozone switched rapidly back and forth between its different resonance forms. More recent experiments have shown that the molecule actually assumes the average of all the resonance forms, with the electrons delocalized over all three oxygen atoms as shown in the following diagram

7 At least seven valid dot structures can be drawn for this molecule. However, some of them require that sulfur have an expanded octet. Therefore, the three structures in which sulfur has exactly eight valence electrons will be the most prevalent.

formal charge=valence e??(nonbonding e?+bonding e?2)

0 Because the formal charges of the individual atoms add to zero, the hydrogen bromide molecule is neutral overall. Formal charges are useful in assessing the feasibility of a bonding arrangement when more than one valid Lewis structure can be written for a molecule.

H - :O: - :F: - :O:: The dash representing a bond. H has no electrons unbonded, O has 4 electrons unbonded, F has 4 electrons unbonded, and O has 6 electrons unbonded where the bond is a lone pair donated from F. Formal Charge: Number Valence electrons - Number of bonds - number of unbonded electrons H = 1 - 1 - 0 = 0 First Oxygen = 6 - 2 - 4 = 0 F = 7 - 2 - 4 = +1 Second oxygen = 6 - 1 - 0 = -1

Structure A is more favored. This is due to Formal Charges. Just remember the formula: Formal Charge = Group # - (Number of unpaired electrons + 1/2 bonded electrons) ...and that Lewis structure always favors the most neutral structure of formal charges which in this case would be(0,0,-1)