1. Atoms

2. Atoms The smallest particle making up elements
Atoms consist of three types of particles
Neutrons with a neutral charge
Protons with a positive charge
Electrons with a negative charge
Mass is measured in a.m.u.
(atomic mass unit)

3. The positive (+) particle is called a
proton +
1 a.m.u.

4. The neutral (no charge) particle is called a
Neutron N
1 a.m.u.

5. The negative (–) particle is called an
electron –
a.m.u. 1
1840

6. In an atom, protons and neutrons
are in the centre (nucleus) and electrons
circle the nucleus in orbits or shells + N – – – – N + + + N N + + N N –
Bohr Model –

7. Bohr model of an Atom Maximum of 2 electrons in First shell (n = 1)
Maximum of 8 electrons in Second shell (n = 2)
Maximum of 8 electrons in Third shell (n = 3) – –
6 P
6 N – – – –

8. C Periodic Table 6 number of protons and electrons Atomic number
12.011 6
Symbol
Atomic Mass
(average)
atomic mass – atomic number = number of neutrons

9. Isotopes Atoms of the same element but different mass number
Boron-10 (10B) has 5 p and 5 n
Boron-11 (11B) has 5 p and 6 n
10B
11B

10. Isotopes of sodium

11. Isotopes and their usage
Bone scans with radioactive Technetium-99
The tritium 3H content of ground water is used to discover the source of the water, for example, in municipal water or the source
of the steam from a volcano.

12. Counting particles Protons: Atomic Number (from periodic table)
Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible)
Electrons:
If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -)
If it does NOT have an equal number of electrons, it is not an atom, it is an ION.

13. Learning Check – Counting
Naturally occurring carbon consists of three isotopes,
12C, 13C, and 14C. State the number of protons,
neutrons, and electrons in each of these carbon atoms.
#p+ _______ _______ _______
#no _______ _______ _______
#e- _______ _______ _______ C 14 6 C 12 6 C 13 6 6 6 6 6 7 8 6 6 6

14. Learning Check – Counting
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X