UNIT 2 REVIEWScience 10

Bohr Diagrams

Electrons appear in shells in a very predictable manner.

There is a maximum of 2 electrons in the first shell, 8 in the 2nd shell, and 8 in the 3rd shell. The period # = # of shells in the atom. Except for the transition elements,

the last digit of the group # = # of electrons in the valence shell

Periodic Trends

Look at Elements on the periodic table and be able to determine

Protons Electrons Mass number Atomic number Net charge (if possible) Of the stable atoms and the isotopes.

Particles Symbol Charge Location

Protons p+ Positive charge

Found in the nucleus

Neutrons 0N

Neutral (no) charge

Found in the nucleus

Electrons e- Negative charge

Found orbiting the nucleus

Naming/Writing formulas of chemical compounds

Name and write formulas for Ionic and covalent compounds

magnesium and nitrogen Magnesium nitride

K3N

K3N A. Step 1 Identify the ions

K=potassiumN=Nitrogen

Step 2 check the charges

K=+1N=-3

Step 3Determine the ratio3 potassium ions for every nitrogen ion

K3N

Balance the charge therefore means that potassium must have a charge of +1 if it takes 3 potssium ions to balance a charge of -3

Or you could cross the subscripts back over to superscripts

K3 N1

K+1 N-3

Potassium nitride

potassium bromide Step 1: determine the charges and

symbolsPotassium=___Charge: +1Bromide=____Charge: -1

Step 2 write superscripts with the symbols and cross over the subscripts

K+1 Br-1

K1 Br1

Answer is: KBrWhen writing names for multivalent

formulas make, cross the subscripts back to superscripts then verify that the charge does exist on the periodic table.

Balancing equations

Go from word equations to skeleton equation

Balance equation using the plan strategy 1.leave anything that appears in more

than one species (or compound) to end Leave elemental forms Balance groups (polyatomic ions) Let the coefficients lead you Classify as S, D, SR, DR, C, N

Example

See overhead

Know how to use the PH charts

Need to know how to determine whether a chemical is an acid or a base according to what colour the indicator has turned

Radioactive Decay

Alpha decay Beta decay Gamma decay

See overhead for example

Nuclear Fission and fusion

Fission Splitting of more massive nucleus into two

less massive nuclei, subatomic particles and energy

Induced or forced Rules 1. mass of numbers on each side of equation

stays the same 2. Sum of the charges on each side of

equation stays the same

Fission

See overhead for example

Fusion

Two low mass nuclei join to form a more massive nuclei

Occurs in the sun

Study Table 7.11 page 321

Fusion

Example see overhead