Atomic Structure & Notation1. Atoms

- Protons- Neutrons- Electrons

2. Atomic Number3. Mass Number4. Atomic Symbols5. Calculations

ATOMSAtoms are the building blocks of all matter.

An atom is made up of smaller bits called subatomic particles which include...

Name Charge Position Mass

ProtonsElectronsNeutrons

+-

neutral NucleusOutsideNucleus 1

01

Atoms – Bill Nye

• Complete the Bill Nye Atoms Worksheet

What is the structure of an atom?

Nucleus• Where the positive charge

resides–Later called the proton

• Later evidence showed the existence of a neutral particle (no charge) –Later called the neutron

What is the structure of an atom?

–Proton (p+)•Has a positive (+) charge•Has a relative mass of 1•Determines the atomic number

•Found inside the nucleus

What is the structure of an atom?

–Neutron (n0)• Has no (0) charge• Has a relative mass of 1• Determines the isotope

–Isotopes are two of the same element with different masses

• Found inside the nucleus

What is the structure of an atom?

• Electron (e-)–Has a negative (-) charge–Has a relative mass of 0 (zero)–Determines the ion (more

later)–Found outside the nucleus

Atomic Number

• Each element is different because they contain different numbers of PROTONS

• The “atomic number” of an element is the number of protons in the nucleus

• # protons = # electrons

Atomic NumberAtomic number of an element is the number of protons in the nucleus of each atom of that element.

Element Atomic # # of protons

Carbon 6 6

Phosphorus 15 15

Gold 79 79

Mass NumberAtomic Mass (Mass Number) is the number of protons and neutrons in the nucleus of an atom:

Mass # = p+ + n0

Atom p+ n0 e- Mass #

Oxygen - 8

- 33 42

- 31 15

8 8 1616

Arsenic 75 33 75

Phosphorus 15 3116

Atomic Notation• Contains the symbol of the element,

the mass number and the atomic number.

X Mass number

Atomic number

Subscript →

Superscript →

Symbol

Atomic Notation Example

the number of

protons in an

atom

the number of

protons and

neutrons in an

atom

He2

4 Atomic mass

Atomic number

Symbol

What is a chemical symbol?

• The chemical symbol tells us what atom it is• It’s a short form (C = Carbon)

• sometimes it’s the Latin short form (Au = Gold)

• Always a CAPITAL LETTER, sometimes followed by one or more lower case letters

• Ex: Oxygen O, Nitrogen N, Sodium Na• *Cobalt – Co *Carbon Monoxide – CO• (Co is an element, CO is a compound)

SymbolAtomic Mass

Atomic Number

Recall - How are P, N, e- related?

• atomic number = # protons

• # protons = # electrons in a neutral atom

• # protons + # neutrons = atomic mass# neutrons = atomic mass - # protons# protons = atomic mass - # neutrons

• How many protons, neutrons and electrons are found in an atom of Cs?

• Atomic number = protons– There are 55 protons

• Mass number = sum of protons and neutrons• Therefore, # Neutrons = Mass Number - # Protons

# Neutrons = 133 – 55 # Neutrons = 78

55Cs

133

Example 1

HHydrogen

1

1

Protons: 1Neutrons: 0Electrons: 1

# protons + # neutrons = atomic mass

NaSodium

23

11Protons: 11Neutrons: 12Electrons: 11

# protons + # neutrons = atomic mass

Example 2 If an element has an atomic number of 34

and a mass number of 78, what is the:

a) number of protons

b) number of neutrons

c) number of electrons

d) complete symbol

= 34 # p+ = Atomic Number

= 44 # n0= Atomic Mass - # p

= 34 # e- = # p+

34 Atomic #= Se Symbol

78 Atomic Mass

Example 3 If an element has 91 protons and 140

neutrons what is the

a) Atomic number

b) Mass number

c) number of electrons

d) complete symbol

= 91 # p+ = Atomic Number

= 231 Atomic Mass = # n0 + # p

= 91 # e- = # p+

91 Atomic #= Pa Symbol

231 Atomic Mass