UPCAT CHEM - COMPOUNDS 2

Element #1

Hydrogen, H

Element #2

Helium, He

Element #3

Lithium, Li

Element #4

Beryllium, Be

Element #5

Boron, B

Element #6

Carbon, C

Element #7

Nitrogen, N

Element #8

Oxygen, O

Element #9

Fluorine, F

Element #10

Neon, Ne

Element #11

Sodium, Na

Element #12

Magnesium, Mg

Element #13

Aluminum, Al

Element #14

Silicon, Si

Element #15

Phosphorus, P

Element #16

Sulfur, S

Element #17

Chlorine, Cl

Element #18

Argon, Ar

Element #19

Potassium, K

Element #20

Calcium, Ca

What is the charge of Group 1 elements (Li, Na, K)?

+1 — they have 1 valence electron which they lose easily (low ionization energy)

What is the charge of Group 2 elements (Mg, Ca, Ba)?

+2 — they have 2 valence electrons which they lose easily

What is the charge of Group 13 (Al)?

+3 — loses all 3 valence electrons

What is the charge of Group 15 (N)?

-3 — needs 3 more electrons to complete octet

What is the charge of Group 16 (O, S)?

-2 — needs 2 more electrons to complete octet

What is the charge of Group 17 (F, Cl, Br, I)?

-1 — needs 1 more electron to complete octet

Atomic mass of H

1 g/mol

Atomic mass of C

12 g/mol

Atomic mass of N

14 g/mol

Atomic mass of O

16 g/mol

Atomic mass of Na

23 g/mol

Atomic mass of Mg

24 g/mol

Atomic mass of S

32 g/mol

Atomic mass of Cl

35.5 g/mol

Atomic mass of Ca

40 g/mol

What is a metallic bond?

Bond formed by electrostatic attraction between metal cations and a sea of delocalized electrons. Metal atoms release valence electrons into a shared sea; stability comes from mutual attraction between cations and electron sea.

What is an ionic bond?

Complete transfer of valence electron(s) from a metal to a nonmetal. Metal has low ionization energy (gives electron), nonmetal has high electronegativity (takes electron). Opposite charges attract — that attraction IS the bond.

What is a covalent bond?

Electrons are SHARED between two nonmetal atoms with similar electronegativities. Both nuclei attract the shared electrons sitting between them — that mutual attraction holds the atoms together.

What is a coordinate covalent bond?

One atom donates BOTH electrons to form a bond with another atom or ion. Result looks identical to a normal covalent bond. Example: N in NH3 donates lone pair to H+ to form NH4+

What is the difference between a compound and a molecule?

Molecule = 2+ atoms bonded together (can be same element, e.g. O2). Compound = 2+ DIFFERENT elements bonded (e.g. H2O). All compounds are molecules but not all molecules are compounds. NaCl is a compound but NOT a molecule (ionic).

What is the name of OH-?

Hydroxide, charge: -1

What is the name of NO3-?

Nitrate, charge: -1

What is the name of NO2-?

Nitrite, charge: -1

What is the name of SO4(2-)?

Sulfate, charge: -2

What is the name of SO3(2-)?

Sulfite, charge: -2

What is the name of CO3(2-)?

Carbonate, charge: -2

What is the name of HCO3-?

Bicarbonate / hydrogen carbonate, charge: -1

What is the name of NH4+?

Ammonium, charge: +1

What is the name of PO4(3-)?

Phosphate, charge: -3

What is the name of MnO4-?

Permanganate, charge: -1

What is the name of Cr2O7(2-)?

Dichromate, charge: -2

What is the name of CrO4(2-)?

Chromate, charge: -2

What is the name of ClO-?

Hypochlorite, charge: -1

What is the name of ClO2-?

Chlorite, charge: -1

What is the name of ClO3-?

Chlorate, charge: -1

What is the name of ClO4-?

Perchlorate, charge: -1

What is the name of C2H3O2-?

Acetate, charge: -1

What is the name of CN-?

Cyanide, charge: -1

What is the name of O2(2-)?

Peroxide, charge: -2

What is the oxidation number of free/uncombined elements (e.g. O2, Fe, Na)?

Always 0 — not bonded to anything, no electron transfer occurs

What is the oxidation number of H in most compounds?

+1 — H is less electronegative than most atoms so it gives its electron away

What is the oxidation number of H in metal hydrides (e.g. NaH, CaH2, LiH)?

-1 — the metal is LESS electronegative than H, so H takes the electron instead and becomes H-

What is the oxidation number of O in most compounds?

-2 — O is very electronegative and pulls 2 electrons toward itself

What is the oxidation number of O in peroxides (H2O2, O2(2-))?

-1 — O is bonded to another identical O atom; neither can steal from the other so they split equally, giving -1 each

What is the oxidation number of F in all compounds?

Always -1 — F is the most electronegative element and always takes electrons, never gives them

What is the oxidation number of halogens (Cl, Br, I) in halide compounds?

-1 — highly electronegative, pulls 1 electron

What is the oxidation number of halogens bonded to oxygen?

Positive — O is more electronegative than most halogens so O pulls electrons AWAY from the halogen. Exception: F is always -1.

What are the octet rule exceptions?

1. Expanded octet: Period 3+ elements (P, S, Cl, Xe) can hold more than 8 electrons using empty d orbitals. 2. Incomplete octet: Be (4e) and B (6e) are stable with less than 8. 3. Duet rule: H can only hold max 2 electrons (only has 1s orbital).

Why can Period 3+ elements expand their octet?

They have empty d orbitals available in their valence shell. Electrons from s or p subshells can be promoted into d orbitals, creating more unpaired electrons for bonding. Period 2 (C,N,O,F) have NO d orbitals so they are strictly limited to 8 electrons.

What is percent composition formula?

% composition = (n x molar mass of element / molar mass of compound) x 100. Where n = number of atoms of that element in the compound.

What is the formal charge formula?

FC = V - N - B/2. V = valence electrons of atom. N = nonbonding electrons (lone pairs on that atom). B = bonding electrons (all electrons in bonds to that atom). B/2 because bonds are shared equally.

Formal charge shortcut (circle method)

Draw circle around atom. Count: lone pair electrons fully + only 1 electron per bond tip inside circle. FC = valence electrons - electrons inside circle. Example: O with 2 lone pairs + 1 double bond: inside circle = 4 (lone pairs) + 2 (bond tips) = 6. FC = 6-6 = 0.

What does formal charge represent?

The charge an atom would have IF bonding electrons were split equally between bonded atoms. Ideal Lewis structure = all formal charges as close to 0 as possible. Sum of all formal charges = overall charge of molecule/ion.