Quote of the Day:

“Expect people to be better than they are; it helps them become better. But don’t be disappointed when they are not; it helps them to keep trying.”

M. Browne

The Atom

• The atom is the basic unit of matter, everything is made up of atoms.

• Atoms are very small, and cannot even be seen by a regular microscope.

• Atoms have no charge (neutral) and are made up of several sub-atomic particles.

Sub – atomic particles: Charge Location Relative

Mass

ELECTRON Negative (-)

Orbiting outside nucleus

Light

PROTON Positive (+)

Nucleus Heavy

NEUTRON Neutral Nucleus Heavy

Diagram of the atom:

What makes atoms different from one another?

• The number of protons, neutrons and electrons an atom has determines what kind of atom it is. Example: The oxygen atom has 8 electrons and protons therefore we know it is an oxygen atom.

• You can determine the number of electrons and protons an atom has by looking at its atomic number found on the periodic table.

Atomic Number

• The atomic number of an element is found on the periodic table. They are arranged in increasing order going from left to right. So Hydrogen has an atomic number of 1, Helium is 2 and so on.

• The atomic number tells us how many protons an atom has. This also tells us how many electrons an atom has, because the number of protons and electrons are balanced. So an atom has the same number of protons as electrons.

To calculate the number of protons and electrons an atom has we must look at the

atomic number.Examples:1. Si 14 electrons, 14 protons2. Rb

37 electrons, 37 protons3. Ag

47 electrons, 47 protons4. N

7 electrons, 7 protons

Isotopes

• All atoms of the same type would have the same number of protons and electrons, but they don’t have to have the same number of neutrons.

• Isotope = atoms of the same type, but having different numbers of neutrons, changing the atomic mass.

Atomic Mass

• The atomic mass on the periodic table a weighted average of the isotopes

Atomic mass = #protons + # neutrons

# Neutrons = atomic mass - # protons

Example:

1. Na has a mass # of 22.98. How many e-, p+ and neutrons does Na have?

e-, p+ = 11

22.98 – 11 = 11.98 12 neutrons

Quote of the day:

“ A man (woman) would do nothing if he waited until he could do it so well that no one could find fault.”

J.H.C. Newman

Electron Shells

• Electrons are found orbiting in shells outside the nucleus

• Bohr Diagrams are a way to represent where the electrons in an atom are located

• 1st shell holds 2 electron

• 2nd shell holds 8 electrons

• 3rd shell holds 8 electrons

• 4th shell holds 18 electrons

Drawing Bohr Diagrams

1. Put the symbol of the element in the centre

2. Start placing electrons in the innermost shells and work outwards

3. Place electrons at N, S, E and W

4. GO back and double if necessary (electrons are usually found in pairs)

Example: Carbon

•Carbon has an atomic number of 6

• Therefore C has 6 electrons

• 2 electrons in 1st shell

• 4 electrons in 2nd shell

Valence Electrons• The outer most electron shell in any atom is

called the valence shell• The electrons in the valence shell are called

Valence Electrons• By looking at the number of valence electrons an

element has we can predict its reactivity.• THE OCTET RULE: Atoms will try to lose, gain

or share electrons to obtain a filled outer level (to form a stable octet).

• Stable octet = 8 electrons

You can tell the number of valence electron that an elements has by looking at the group

numberGroup 1 has 1 valence electronGroup 2 has 2Group 13 has 3Group 14 has 4Group 15 has 5 Group 16 has 6Group 17 has 7Group 18 has 8

Electron Dot Diagrams

• An easier way to represent the number of valence electrons an atom has is to use electron dot diagrams.

• Electron dot diagrams show only the valence electrons

Predicting Chemical reactivity:

• By looking at the number of valence electrons an element has we can predict its reactivity.

• Atoms will try to lose, gain or share electrons to obtain a filled outer level, or to form a stable octet (8 electrons)

Quote of the day:

“To be upset over what you don’t have is to waste what you do have.”

K.S. Keyes

Ions

• When atoms gain or lose electrons they form something called IONS. Energy is released when this happens.

• Ions are electrically charged atoms. (positive or negative)

Cations (+)

• CATIONS: are positively charged ions. Cations are formed when an atom loses electrons.

• Metals and Hydrogen form cations

• Ex: Na lose 1 electron

Na1+

Anions (-)

• ANIONS: are negatively charged ions. Anions are formed when atoms gain electrons.

• Most non-metals form anions.

• Ex: Cl gains one electron

Cl1-

Charges of Ions

Group 1 loses 1 electron = +1Group 2 loses 2 electrons = +2Group 13 loses 3 electrons = +3Group 15 gains 3 electrons = -3Group 16 gains 2 electrons = -2Group 17 gains 1 electron = -1

Group18 has a full outer shell = very stable

What kind of ions do the following elements make? (either + or -)

a) O

b) Br

c) Ca

d) Se

e) Mg

f) B

g) Cl

h) C

Answers:

a) O (–) h) C can be both (+) (-)

b) Br (-)

c) Ca (+)

d) Se (+)

e) Mg (+)

f) B (+)

g) Cl (-)

Compounds

• Compound = a pure substance made up of two or more elements that are chemically combined

• Ionic Compounds = substances composed of cations and anions

• Ionic Bond = the attraction between positive and negative

Making “Ionic Compounds”Activity

• Groups of 2 or 3

• Gather a handful of paper squares

• Write the symbols for the ions on the squares Positive in one color and Negative in another

Label each of the following on squares:

• H+

• Li+

• Na+

• K+

• Be2+

• Mg2+

• Ca2+

• F-

• Cl-

• Br-

• I-

• O2-

• S2-

• Se2-

• N3-

• Fe2+

• Co3+

• Cr2+

• Cu2+

• Al3+

• Ni2+

• P3-

• As3-

The challenge:(only one copy per group needed)

• By using your paper squares, see how many different combinations your group can make that sum to zero

• Always write the cation (+) then anion (-)

• Use subscripts to represent the # of ions

Examples:

• H+ Cl- HCl

• H+ H+ O2- H2O

Noble Gases

• Group 8A (He, Ne, Ar, etc.)

• Have a full valence shell (complete octet)

• They neither want to gain or lose electrons

• Therefore, DO NOT form IONS

IONs Summary:

• Alkali metals form 1+ cations• Alkaline earth metals form 2+ cations• Noble gases don’t form ions• Halogens form 1- anions• Group 16 form 2- anions to staircase• Group 15 form 3- anions to staircase• Transition metals, and metals under staircase,

form more than one cation so look at #2 periodic table. (table of ions)

ex: Copper can form 2+ and 1+ cations