Atomic Structure

Vocabulary & People 

orbit valence

Amu (µ) atomic mass atomic number

Bohr

S1-2-04 Explain the atomic structure in terms of subatomic particles and define atomic number and atomic mass.

S1-2-05 Assemble or draw Bohr atomic models.

Colour Elementgreen copper

red strontium

purple potassiumlavender Lithiumyellow sodium

• Emitted light was from excited electrons

5. Bohr (1913)

“Flame Test” experiments show heated elements emit a unique pattern of colour.

This unique colour signature can be used to identify elements in mixtures or compounds

Hypothesis:Electrons move in organized circular paths of different distances around a nucleus.

Orbit: location of electron motion around a nucleus.

Only a specific number of electrons fill each orbit

Bohr reasoned that random electron

movement cannot produce the same

unique colour pattern EVERY TIME

1st – holds two electrons (e-)2nd – holds eight e-

3rd – holds eight e-

• Electrons occupy the closest orbital first

Bohr’s model is called the “planetary” model

• Elements have a different number of electrons

Valence:• Last (outer) atom orbit• All electrons in last orbit - valence electrons

The number of valence electrons an atom has determines how the atom chemically reacts

Hydrogen has a total of 1 e- (1 valence e- )

Boron has a total of 5 e- (3 valence e- )

Neon has a total of 10 e- (8 valence e- )

Atoms Neutron (no) – nucleus particle with no charge. Proton (p+) – nucleus particle with (+) charge. Electrons (e-) –particles in orbits with a (-) charge.

• Protons have a mass of 1 Atomic Mass Unit (μ)• Neutrons are the same size - also 1 μ• Electrons are considered zero mass

NeutronsProtons

electrons

+-

Amu is just a unit to measure very small masses equal to

1.6605 x 10-24 grams

The information on the Periodic Table will help us build atomic models – “Bohr” models

Atomic mass• Larger value – total mass in Amu• Equals the number of p+ and no in the nucleus• Round off the value

Since protons and neutrons each weight 1 amu –there must be 4 protons and neutrons in the nucleus of a

helium atom to weigh a total of 4 amu

Important points:1.No TWO elements have the same number of

protons.2.The number of protons in an element does

NOT change.

Atoms can lose and gain neutrons and electrons – since protons have NEVER been shown to change we use this to

identify elements

Atomic number• Smaller value – no units• Equals number of protons• p+number is used to identify an element

Since atoms are neutral (equal number of protons and electrons) – you can use Atomic number to find the

number of protons OR electrons in the atom

PROTONS Atomic Number = 2NEUTRONS A.mass – A.number = 4 – 2 = 2ELECTRONS Same as Protons = 2

Atomic Mass Atomic Number (Protons + Neutrons) (Protons)

Sulfur (S)

How many protons are there in one atom of Sulfur?Atomic number 16 - 16 p+

How many electrons in one atom of Sulfur?

How many neutrons in one atom of Sulfur?

How many protons in 3 atoms of Sulfur?

Atoms are neutral - 16 e-

Atomic mass 32 32-16 = 16 no

3 x 16 = 48 p+

An atom is found with 19 protons:

What element is this?Potassium

How many electrons in one atom of Potassium?

How many neutrons in one atom of Potassium?

How many protons in 10 atoms of Potassium?

Atoms are neutral – 19 e -

At mass – At number 39 – 19 = 20 no

10 x 19 p + = 190 p +

Drawing a Complete Bohr Atom:

1. Determine the number of no, p+, e- in the atom.2. Draw the nucleus.3. Label the #of protons and neutrons.4. Add orbits and fill with the appropriate # of e-.

7p+

7no

Nitrogen (N)p+ : 7no : 14 – 7 = 7 e- : 7

11p+

12no

Sodium (Na)

p+ : 11

no : 23 – 11 = 12

e- : 11

CAN YOU ANSWER THESE QUESTIONS?S1-2-04How do you use atomic mass and atomic number to identify parts of the atom?

S1-2-05How do you draw an atom using the Bohr model?

Vocabulary & People 

orbit valence

Amu (µ) atomic mass atomic number

Bohr