5.2 The Structure of the Atom

The Atom

The atom is made up of three subatomic particles:

Protons (p+) Electrons (e-) Neutrons (no)

The protons and neutrons are found in the nucleus at the centre of the atom.

The electrons are found “orbiting” around the nucleus in specific energy levels.

The Subatomic Particles

Particle Location Charge Mass

Proton nucleus +1 1

Electrons outer shells -1 0

Neutrons nucleus 0 1

Shows: Atomic number

the number of protons in the nucleus of an atom The atomic number identifies the atom as a particular

element

Mass Number The number of protons and neutrons in an atom

Standard Atomic Notation

Uses a standard symbol to represent the element (ex. H for hydrogen, Li for lithium)

The AtomCalculating the Number of SubatomicParticles:

Atomic number = number of protons

Mass number = number of protons + number of neutrons

Number of neutrons = mass number – atomic number

Number of protons = number of electrons (neutral atom)

Activity 5-4, p. 189

Read the activity and complete #1-4NOTE: for number 3, do not use Appendix A,

instead use the periodic table on p. 197, the mass number is the number under the symbol, rounded. Ex. zinc 65.4 = 65.

Answers to Activity 5-4

1. carbon = C, hydrogen = H, nitrogen = N

Rule: use the first letter (capital) of each element

2. a. Calcium = Ca, use the first two letters, first letter only capitalized.

b. C cannot be used as it is already used for carbon

3. silver (argentum) = Ag, gold (aurum) = Au, copper (cuprum) = Cu, iron (ferrum) = Fe, mercury (hydrargyrum) = Hg, lead (plumbum) = Pb, tin (stannum) = Sn

Identify rules….

4. Next slide…

Standard Atomic Notation

Name of Element

Atomic Number

Mass Number

Number of Electrons

Number of Protons

Number of Neutrons

126C Carbon 6 12 6 6 6

6530Zn zinc 30 65 30 30 35

Sulfur 16 16

Calcium 40 20

nitrogen 7 14

Bohr Rutherford Diagrams

Show the quantities and locations of protons, electrons and neutrons in an atom (used for the 1st 20 elements)

Atomic Number = # of protons # of neutrons = Mass Number – Atomic Number # of electrons = # of protons in a neutral atom

For an atom of Helium: Atomic # = # of protons = 2 # of neutrons = Mass Number – Atomic Number

= 4 - 2

= 2 # of electrons = # of protons = 2

Bohr-Rutherford Diagram for He

2p+

2n°

2e- # of electrons in 1st orbital (energy level) Max = 2

# of protons (p)# of neutrons (n)Nucleus

helium

Bohr-Rutherford Diagram for K

19p+

20n°

2e-

8e-

Nucleus

8e-

1e-

# of electrons in 2nd orbital (energy level) Max = 8

# of electrons in 1st orbital (energy level) Max = 2

# of protons (p)# of neutrons (n)

# of electrons in 3rd orbital (energy level) Max = 8

# of electrons in 4th orbital (energy level) Max = 8

Potassium

Isotopes

Most atoms of an element have the same number of neutrons

A few will have a different number of neutrons Ex. Most Li atoms have 3 protons and 4 neutrons

Mass Number = 7

Some have only 3 neutrons Mass Number = 6

Atoms that have the same number of protons but different numbers of neutrons are called isotopes.