(We will discuss why the table has this form in more detail in Chapter 8.)

General principles:

Elements in the same column have similar chemical properties.

Reactivity gets more varied as you go down a column.

Alkali metals

Soft metals, very reactive, burn (or explode) in air

Form Li⁺, Na⁺, K⁺, etc. ions

Alkaline earth metals

Be, Mg, not so soft

Form Be²⁺, Mg²⁺, Ca²⁺m etc. ions

Transition elements

All metals

Form wide variety of ions and complex ions

B group

B is metalloid, Al, Ga, etc. are metals

Al³⁺, etc. ions

C group

C is nonmetal, Si and Ge are metalloids, Sn and Pb are metals

Metals form Sn⁴⁺, Pb⁴⁺, ions, but also Sn²⁺, Pb²⁺ ions

Form compounds with H: CH₄, SiH₄, GeH₄, SnH₄, PbH₄ compounds

N group

N and P are nonmetals, Bi is a metal

Compounds with H: NH₃, PH₃, AsH₃, SbH₃, BiH₃

O group

Form O^2- , S^2- , Se^2- , etc. ions

H₂O, H₂S, H₂Se, H₂Te, etc

Halogens (acid formers)

Form F- , Cl- , Br- , I- , etc. ions

HF, HCl, HBr, HI, etc. gases soluble in water to form acids

Noble gases

Very unreactive

No compounds of He and Ne, Ar (Aug 2000?), Some of Kr and Xe

Recall: Two classes of pure substances

Elements – can’t be broken down into simpler substances

Compounds – can be broken down into simpler substances

Smallest particle of an element = atom

(Some exceptions in nature.)

Smallest particle of a compound = molecule

(Ionic compounds?)

Types

empirical

molecular

structural

perspective

model or graphics

Examples

NH₃

b sugar (6 C, 12 H, 6 O atoms)

For example

.

Composition of b sugar

C = 6 ´ 12.01 amu = 72.06 amu

H = 12 ´ 1.008 amu = 12.10 amu

O = 6 ´ 16.00 amu = 96.00 amu

total = 180.2 amu

% C = 72.06/180.2 ´ 100 = 39.99

% H = 12.10/180.2 ´ 100 = 6.71

% O = 96.00/180.2 ´ 100 = 53.27

N = 14.01 amu

H = 3 ´ 1.008 amu =

NH₃ =

We can go the other way. Given the percent composition we can find the empirical formula. We will do this a little later in the Chapter.

Charges on Monatomic Ions

Examples

Li

Sr

La

(the middle gets complicated, look at it later)

As

S

I

Xe

Naming positive ions is easy

element forms only one ion:

Ca²⁺ = calcium ion

element forms more than one ion:

Cu⁺ = copper I ion

Cu²⁺ = copper II ion

Naming negative ions is almost as easy

(Drop the last part of the element name and add "ide.")

Br- = bromide ion

Te^2- = telluride ion

N- ³ = nitride ion (not too common)

C- ⁴ = carbide (exists, but rare)

Polyatomic Ions

These you just have to memorize. See Table 3.1, page 110 in text.

Formulas of Ionic Compounds

Rule: The compound must be neutral (compound has no net charge)

Examples:

K⁺ and S^2-

Sr²⁺ and O^2-

La³⁺ and SO₄^2-

If we know the names of the ions we can name the ionic compound

Consider words that name numbers of things:

pair

dozen

score

ream

The mole is a word like this, but it stands for a very large number of things:

1 mole = 1 mol = 6.0221367 ´ 10²³ "things"

"Things" could be anything, people, ants, grains of sand, etc. But we usually use it to count atoms and molecules (and sometimes electrons).

This number is called Avogadro’s number.

For our purposes, it is defined such that 1 mol of carbon-12 atoms has a mass of exactly 12 g. Recall that 12 amu is the mass of one carbon-12 atom.

Then 1 mol of oxygen-16 atoms would weigh 15.9949 g since one atom of oxygen-16 weighs 15.9949 amu.

By extension, one mole of "average" carbon atoms would weigh 12.011 g.

We can look at the average mass of atoms of an element in two ways:

1 The average mass of atoms of the element

So, for carbon, we can think of the 12.011 as having two possible units

1 The mass on one average atom in amu

2 The mass of a mol of atoms in g/mol

I will always refer to quantities like this as the atomic weight

Extend this concept to compounds and molecules.

The "molecular weight" is the sum of all the atomic weights in the molecule.

Examples

H₂

H₂O

C₆H₁₂O₆

NaCl

All of these number have units of g/mol or amu, depending on what we are doing with the number.