Atomic Structure

SOL 6.4

Parts of an Atom

• Protons• Neutrons• Electron

Protons

• Have a positive (+) charge• Are located in the nucleus• Give an atom its identity• Are equal to the atomic number

Lithium has an atomic number 3. Therefore, Lithium has 3 protons. Another way of phrasing this fact is, any atom with the atomic number 3 MUST be Lithium.

Neutrons

• Have NO charge- they are neutral

• Are located in the nucleus

• Remember the ‘NEWS’ about atoms-Neutral neutrons are located in the nucleus!

The mass number of an atom is calculated by adding protons + neutrons. Atomic mass is an average of the masses of all

the atoms of that element.

The atom to the left has 3 protons and 3 neutrons.3 + 3 = 6The mass number of this atom is 6.

Isotopes are the SAME element, but have different numbers of NEUTRONS and therefore different mass numbers.

Electrons

• Are the smallest, lightest particle• Are located outside the nucleus in the elctron

cloud• Have a negative charge• Are equal to the number of protons in a

neutral atom

“I don’t care”

Bohr model Electron cloud

model

Models of the Atom

9

17

Let’s Practice!What is the atomic number?

What is the mass?How many protons? How many neutrons? How many electrons?

Element

• An element is the simplest form of matter. It is made up of only ONE type of atom.

• An element ALWAYS has the same number of protons and same atomic number. However, it may have different numbers of neutrons and different masses (isotopes).

• Elements are represented by chemical symbols. Chemical symbols are ALWAYS Capitalized (one letter) or Capital lower case (two letters).