Download Drawing Atomic Structure

Physical Science
Chapter 17: Atoms and the Periodic Table
Atomic Structure Notes
Review
What is an atom?
An atom is the smallest particle of an element that still retains the properties of that element.
Atomic Symbol
- The shorthand abbreviation that is used to identify an element (element name)
- Atomic symbols have
o A capital letter at the beginning of the symbol (all symbols have this)
o Some have a lower case letter after the capital letter
 Be careful! The letters of the atomic symbol do not always match the name of
the element
o
o
Examples:
Hydrogen
Helium
Magnesium
Potassium
Iron
Sodium
__________
__________
__________
__________
__________
__________
Label the element name and atomic symbol on the diagram above
Nucleus (discovered by Rutherford in 1911)
- The center of the atom
-
Contains a majority of the mass of the atom (99.9%), but a small portion of the volume
-
Relative size of the nucleus:
IF the atom was the size of a stadium, the
nucleus would be the size of a marble.
-
The nucleus contains:
o
Protons

Have a positive charge

Have a mass of 1.6726 x 10-24 grams or 1 atomic mass units (amu)

The number of protons determines the type of atom that you have!! (If you
change the number of protons, you change the element!)

We call this the atomic number

Label the atomic number on the diagram above
Complete the table below. Use the Periodic Table on p. 518 to help you.
Element
Atomic Symbol
Atomic Number
# of Protons
Copper
Cu
29
29
Bromine
Br
35
35
Lead
Pb
82
82
o
Neutrons (Discovered by Chadwick in 1932)

Are neutral, which means they have no charge

Have a mass of 1.6749 x 10-24 grams or 1 atomic mass units (amu)

To determine the number of neutrons in an atom, you need to know the atom’s
mass number

Mass number: the sum of the number of protons and the number of
neutrons in the nucleus of an atom

# of Neutrons = Mass Number – Atomic Number

If you are given the mass number and the number of neutrons, how
can you figure out the number of protons?
-
o
Subtract the number of neutrons from the mass number
Protons and Neutrons can both be broken down even farther into quarks. More info on pg. 508
Electrons (Discovered by JJ Thompson in 1904)
- Have a negative charge
-
Have a very small mass (approximately 9.1093 x 10-28 grams or 0.00055 amu)
-
In a neutral atom, the total number of electrons equals the number of protons
-
Can be found in electron clouds surrounding the nucleus (Developed in 1926)
o
Electrons are so small and move so quickly that it is impossible to determine their
exact location (fan example) however we can predict it based on probability
o
The electron cloud is approximately 100,000 times larger than the nucleus
o
Each electron cloud has a different amount of energy
o
The electron clouds closest to the nucleus have the lowest amount of energy, and the
electron clouds furthest from the nucleus have the most energy
o
Electrons fill the energy levels from the inner levels to the outer levels

Each level can hold a specific number of electrons
32 electrons
18 electrons
8 electrons
2 electrons
*Note: Remember the Bohr model (proposed in 1913 by Niels Bohr) is no longer the accepted model
for the atom, however it is easier to understand the behavior of electrons and where they are located if
we imagine the electron clouds as orbits.
Drawing Atomic Structure
Draw a diagram of a neutral atom for the element that contains 2 protons and has a mass number of 4.
Element name: Helium
Protons: 2
Electrons: 2
Neutrons: 2
p+= 2
n =2
Draw a diagram of a neutral atom for the element that contains 12 protons and has a mass number of 24.
Element name: Magnesium
Protons: 12
Electrons: 12
Neutrons: 12
p+= 12
n = 12
Draw a diagram of a neutral atom for the element that contains 9 electrons and has a mass number of 19.
Element name: Fluorine
Protons: 9
Electrons: 9
Neutrons: 10
p+= 9
n = 10
Isotopes
 Atoms of the same element that contain the same number of
protons, but a different number of neutrons

Because isotopes have a different number of neutrons, they also
have different mass numbers.

Most elements have more than one isotope, and therefore have
an average atomic mass.
o

The average atomic mass is the weighted average mass of an element’s various isotopes (takes
into consideration which isotopes are more abundant than others).
 The average atomic mass can be found on the Periodic Table. Label this on the diagram
on the first page.
Isotopes can be symbolized in a few ways:
1) Atomic symbol, mass number, and atomic number
Mass number
Atomic number
14
6
C
Atomic Symbol
2) Atomic name or symbol with a hyphen and mass number
Carbon-14 or
C-14