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nucleus of atom
+
ProtonsOSITIVE
+ NeutralO
CHARGE
ElectronsN
GATIVE
-
+
The Atom - Charge
Charge can be Neutral, Positive or Negative
Charge is equal to 0
Charge is equal to +1
Charge is equal to -1
What do you noticeabout the periodic table?
The whole numbers (above the element symbol) increase across the rows.
3 4 5 6 7 8 9 10
The whole numbers are the Atomic Numbers.
Carbon has an atomic number of 6.
Carbon has 6 protons.
The atomic number (number of protons) determines the identity of the element.
B
5
10.811
Boron
C
6
12.011
Carbon
N
7
14.007
Nitrogen
So, if you change the number of protons, you change the element.
What else do you noticeabout the periodic table?
There are decimal numbers below the element symbol.
6.941 1.0002 10.811 12.011 14.007 15.999 18.998 20.180
The decimal numbers are the Atomic Masses.
2.0164186 amu
+
0 amu
Mass of an atom with one Proton, one Neutron and one Electron.
Mass of an atom with one Proton and one Neutron.
2.01587 amu
Electrons are too small to change the mass of the atom.
Protons and Neutrons determine the Atomic Mass.
– Isotopes = atoms of the same element that have different numbers of neutrons
Carbon-126 neutrons +
++ ++ +
7 neutrons
Carbon-13
+++ +
+ +
12 amu 13 amu
Mass of Carbon-12 Isotope is 12 amu
Mass of Carbon-13 Isotope is 13 amu
Carbon has an Atomic Mass of 12.011.
12.011 rounds to 12. So, the Mass Number of carbon is 12 amu.
Since the mass of each proton and each neutron is 1 amu and the atomic mass of Carbon is 12 amu, there are 12 protons and neutrons in a Carbon atom.
AtomicMass
AtomicNumber
AtomicNumber
•For example: Carbon has 6 protons.
•For example: Carbon has 6 electrons.
AtomicMass
For example: Carbon has a Mass Number of 12 and an Atomic Number of 6.
12 – 6 = 6 So, Carbon has 6 neutrons.
Do you notice anything elseabout the periodic table?
There are roman numerals above each column.
IA
IIA IIIA IVA VA VIA VIIA
VIIIA
The roman numerals are the Group Numbers.
Group IIA elements =2 valence electrons
