Atoms
What are atoms?
• The basic building blocks of matter
• They make up everything found in the world around us.
• You are even made up of atoms!
• Atoms are made up of three subatomic particles:
• Protons
• Neutrons
• Electrons
• Each of these particles carries a charge
• Take a moment to think about what charge you
believe each of these particles carry.
Protons and Neutrons
• Protons carry a positive
charge
• Neutrons carry a neutral
(no) charge
• The nucleus of the atom
is made up of a mass of
protons and neutrons
Electrons
• Carry a negative charge
• Circle the nucleus forming
the electron cloud
• Very small compared to
the other parts of the
atom and move so fast it
is difficult to pinpoint
their location
Balance
• The number of protons and electrons in an atom are
usually equal
• This causes the atom to have a neutral (no) charge
• What would happen if there were more electrons
than protons?
• More protons that electrons?
Valence Electrons
•
The electrons in the
outermost shell of an atom
•
This shell is called the
valence shell
•
The only electrons that
react with other atoms
How to find the valence electrons
• Take out the copy of the periodic table and a pencil
• Number the columns of the periodic table
• Not including the ten columns of the transition
metals in the middle block
• Starting from the left label the first column 1, the
second column 2, the thirteenth column 3, the
fourteenth column 4…until you are to the right side
of the table and you have labeled the eighteenth
column 8
1
2
*except He (it has 2 valence electrons)
3
4
5
6
7
8*
How to find the valence electrons
The number that you have put above the column
represents the number of valence electrons of the
elements in that column
The only exception is He which only has two valence
electrons but is located at the far right due to
similarities in chemical behavior to that group
What is the number of valence
electrons for the following atoms?
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Boron (B)
Chlorine (Cl)
Potassium (K)
Strontium (Sr)
Astatine (At)
Neon (Ne)
Bromine (Br)
Sodium (Na)
What is the number of valence
electrons for the following atoms?
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Boron (B)
Chlorine (Cl)
Potassium (K)
Strontium (Sr)
Astatine (At)
Neon (Ne)
Bromine (Br)
Sodium (Na)
•
•
•
•
•
•
•
•
•
•
•
•
4
1
6
5
3
7
1
2
7
8
7
1
Ion
• An atom in which the total number of electrons is
not equal to the total number of protons
• The atom has a net positive or negative electrical
charge
Determining an Atom’s Charge
• Atomic number - number of electrons actually
present in the atom = overall electrical charge of
atom
• Atoms are “happiest” with full valence shells (8
electrons)
• They will interact with other atoms and gain or lose
electrons to achieve this
Determining an Atom’s Charge
• Elements in groups 1 – 3 “find it easiest” to loose
electrons and thus make positive ions or cations
• Elements in 5 – 7 “find it easiest” to gain electrons
and thus make negative ions or anions
• The number of electrons gained or lost will
determine the charge
•
i.e. loss of 1 electrons = +1 charge
Example
• Using a periodic table determine what charge the
following elements would likely have.
• Na
• As
• Br
• S
• Mg
• B
Answers
• Na: +1
• As: -3
• Br: -2
• S: -1
• Mg: +2
• B: +3