Atomics

Chemical Formula

● Represents the elements in a compound and their proportion

● Examples

○ NaCl - Sodium Chloride ( 2 atoms)

○ C6H12O6

- Glucose (24 atoms)

○ H2O - Water (3 atoms)

Atoms

● Smallest unit of matter

● Can’t be broken down by chemical

means

● Has all of the physical and chemical

properties of the element it makes

● Contains a nucleus with protons

and neutrons and outer shell(s) with

electrons

Protons, Neutrons, and Electrons

● Protons- found in the nucleus

○ Have a positive (+) charge

○ Mass = 1 amu

● Neutrons- found in the nucleus

○ Have no charge / are neutral (0)

○ Mass = 1 amu

● Electrons- found in the shells / outer

clouds

○ Have a negative (-) charge

○ Mass = negligible

When the number of protons = number of

electrons there is no net charge

Elements

● Pure substances made up of

only one type of atom

○ Can be found on the periodic table

(elements)

● Each elements has:

○ An atomic number which is

distinguished by the number of

protons in their nucleus

○ An atomic symbol

○ Atomic mass (# protons + #

neutrons)

Practice

Isotopes

● Contain a different number of neutrons

● Changes the atomic mass BUT NOT

THE ATOMIC NUMBER

● Results in an atom that is unstable

(radioactive)

Three isotopes of Li (Lithium)

All have atomic number of 3

Masses are 6, 7, or 8 depending on neutron #

Average atomic mass

● Average atomic mass takes into

consideration the weighted average of all

naturally occurring isotopes of an element

● Example: There are 3 naturally occurring

isotopes of carbon

○ C-12, C-13, and C-14

● The 12, 13, and 14 represent the different

masses of the isotopes

● The average atomic mass of carbon is

12.011 (this is not the average of the

numbers 12, 13, and 14, but rather the

average of all the isotopes and their

abundance

○ This takes into account that C-12 is the most

abundant

Ions

● When the charge of an atom /

molecule is not neutral

○ Number of protons DOES NOT

equal the number of electrons

○ Number of electrons changes

(gain/loss)

○ ATOMIC NUMBER AND ATOMIC

MASS DO NOT CHANGE

○ When an atom loses electrons, it

becomes positive (cation)

○ When an atom gains electrons, it

becomes negative (anion)

Li+ protons = ___ neutrons = ___

Ca2+ protons = ___ neutrons = ___

- protons = ___ neutrons = ___

3- protons = ___ neutrons = ___

Electron Configuration

● The arrangement of electrons in an atoms

energy levels/orbitals within the cloud.

● Furthest shells from the nucleus have the

most energetic electrons and available

room

● Each shell has a max number of electrons

○ Elements 1-20 (2-8-8)

○ Elements 20+ (2-8-18-32-60)

● Fill from the inside and then move out as

each shell reaches its max (for ground state)

○ For example: Sodium has 7 electrons so

2 go in the first shell and then 5 go in the

second shell

Excited State Electrons

● If electrons become excited, they move from the ground state to a shell

further from the nucleus (furthest shell = more energy)

● For example, for Silicon (Si), if electrons normally fill shells as 2-8-4 in the

ground state, the excited state electron configuration could be 2-7-5

○ One of the electrons in the second shell moved to the third shell

further from the nucleus

■ What would the excited state electron configuration be for a

neutral atom of chlorine (Cl)?

■ What about oxygen (O)?

Outermost Electrons (Valence)

● The number of electrons in the last shell/energy

level (furthest from the nucleus)

● Determines the bonding properties of the atom

○ Each atom “wants 8” (we will learn more about this

later)

Bohr Model / Lewis Dot Diagram ● A Bohr Model is a representation

of what shells all negative

electrons are in for a specific atom ○ Furthest shells from the

nucleus have the most

energetic electrons and

available room

● A Lewis Dot Diagram is the

elemental symbol surrounded by

dots or X’s representing the

outermost electrons only for a

specific atom

Bright line Spectrum (wavelengths) Electromagnetic

History