The Atom
The Atom
• Element – is matter composed of 1 type of
atom
– Examples: Carbon, Oxygen
• Atom – the smallest piece of matter
– 2 main areas: the nucleus, electron cloud
– Made up 3 subatomic particles
• Proton, Electron, Neutron
Parts of the Atom
• Nucleus
– center of atom, overall positive
charge
– Contains:
• Protons with +1 charge,
1 amu (mass)
– Number of Protons is unique to
each element
• Neutrons with neutral charge,
1 amu (mass)
Parts of the atom
• Electron Cloud
– Surrounds nucleus,
overall negative charge
– Contains:
• Electrons with -1 charge,
0 amu (mass)
– Used to form Chemical Bonds with
other elements
Practice
Subatomic
Particle
Protons
Neutrons
Electrons
Charge
Location
Mass
Reading the Periodic Table
28
Ni
Atomic Mass
58.71
Nickel
Element
Name
Atomic
Number
Atomic Symbol
Atomic number
• The Period Table is organized according to the
atomic number of each element.
• Identifies each element ( like your ss#)
• Atomic number = the number of protons
– Because atoms have an overall neutral charge, …
• This means the # protons = # electrons
Reading the Periodic Table
28
So Nickel has
28 protons
28 electrons
Ni
58.71
Nickel
Atomic
Number
Atomic Mass
• = number of protons + number of neutrons
Example 1, if your atomic number is 28 and
your mass number is 58.71…
28
– # of protons?
– # of electrons? 28
– # of neutrons? 58.71 = 28 + N
30.71
Example 2
19
How many
-protons? 19
K
-electrons? 19
39.0983
-neutrons? 20
Potassium
Ions
• = atoms that have lost or gained
electrons.
– Atoms with a charge.
• 2 Types
– Cation = Positive ions
• lost 1 or more electron
– Anion = Negative ions
• gained 1 or more electron
Cations
Li
+++
- - -
3 protons
3 electrons
Li+
+++
- -
3 protons
2 electrons
Anions
9 protons
9 electrons
F
+++++++++
- - - - - - - - -
F-
9 protons
10 electrons
+++++++++
- - - - - - - - - -
Practice Ions
• S -2 Sulfur with -2 charge
– Protons? 16
– Electrons? 18
• Al +3 Aluminum with +3 charge
– Protons? 13
– Electrons? 10
• K+ Potassium with +1 charge
– Protons? 19
– Electrons? 18
Isotopes
Isotopes
• = Atoms of the same element but different
mass number (different # of neutrons).
– To write: Element name – Mass Number
Carbon-12
has 6 p and 6 n
Carbon-14
has 6 p and 8 n
Isotopes of Carbon
• Normally carbon is: Carbon-12
– These carbon atoms have 6 neutrons
• Some carbon atoms may have 7 or 8
neutrons
• Carbon-13
• Carbon-14
• These atoms are still carbon, but we call
them isotopes
Carbon Isotopes
Neutron
+
Electrons
Nucleus
+
+
+
+
+
Nucleus
Proton
Proton
Nucleus
Carbon-12
Neutrons 6
Protons
6
Electrons 6
+
+
+
+
Neutron
Electrons
+
+
Carbon-14
Neutrons 8
Protons
6
Electrons 6
Nucleus
Mass Number vs Average Atomic Mass
• Mass number
– number of protons + neutrons
– But, refers to one specific isotope
Carbon - 12
• Average Atomic mass
– number of protons + neutrons
– But, an average of all isotope’s masses
– What you see on periodic table
Calculate Average Atomic Mass
Avg.
(mass)(%) + (mass)(%)
Atomic =
100
Mass
• Chlorine has 2 isotopes. Chlorine-35 occurs at
75.53% and Chlorine-37 occurs at 24.47%.
What’s the average atomic mass?
• Avg Atomic Mass = (35)(75.53) + (37)(24.47)
100
• Avg Atomic Mass= 35.49 amu