NAME ______________________________________
DATE ____________ PER ____ DOC ___
Atomic Structure Notes
All matter is made of ______________. The word “atom” comes from the Greek word
“atomos” meaning ________________________. An
atom is the smallest part of an
____________________. It is 1 million times smaller
than the width of a piece of hair. There are 115
different kinds of atoms. Each atom is identified by its
number of _________________, also called the atomic
__________________. Each type of atom is
represented as an element on the Periodic Table.
Parts of an Atom
Part Name
Location
Mass
Charge
Atomic Mass and Charge

Most of the mass of an atom is in the ____________________ since that is where the
protons and neutrons are.
Formula for calculating Atomic Mass:

The unit for atomic mass is ______________ _____________ ______________.
The Periodic Table does not list the number of neutrons, but you can calculate them by
rearranging the Atomic Mass formula:
Since an atom has the same number of protons and electrons, an atom has a ______________
charge.
Electron Cloud





The electron cloud takes up most of the space of an atom but this space is mostly
_________________.
Electrons are arranged into energy levels called _______________.
When a shell is full, we say it is _____________________.
Electrons far from the nucleus have the most energy.
Electron Configuration

This describes how electrons are arranged in the shells.
K shell- closest to the nucleus
holds ______ electrons
lowest energy level
L shell- holds up to ____ electrons
M shell- holds up to either ______ or ______ electrons
N shell- holds up to either 18 or 32 electrons
Example:
Sodium (Na) has an electron configuration of 2-8-1.
Sodium has:
2 electrons in the K shell
8 electrons in the L shell
1 electron in the M shell
Now you try!
Chlorine has an electron
configuration of ____-____- ____.
____ electrons in the K shell
____ electrons in the L shell
____ electrons in the M shell
Which element is this a picture of?
Valence Electrons
 the electrons in the last shell (farthest from the nucleus)
 these are very important because they form chemical ___________ with other atoms
and give an element its _________________ properties
Special Cases!
1. Ions- when an atom gains or loses an electron, it develops a charge.
An ion’s charge is __________________ when it gains an electron.
An ion’s charge is __________________ when it loses an electron.
What happens when a positive sodium ion and a negative chlorine ion approach each
other?