What is an Atom?

What is an Atom?
• Atom: Smallest unit of all
matter (building blocks)
• 3 Main Parts:
– 1)) Proton ((+))
– 2) Neutron (0)
– 3) Electron (-)
• Protons & Electrons
usually equal
• Elements (substance made
of only 1 type of atom) are
id ifi d on the
identified
h Periodic
P i di
Table (page R36)
Reading the Periodic Table
What’s the:
A) Atomic number of
Beryllium?
4
B) Atomic mass of Beryllium?
9
• How many neutrons does
• Atomic Number:
Carbon contain?
Number of protons (+)
determines the type of
atom
• Atomic Mass: Combined
protons and neutrons
inside the nucleus
• Electrons orbit the nucleus
in “energy
energy levels
levels”
st
• 1 level: closest to nucleus
(holds 2 electrons)
• 2nd level: holds 8 electrons
• 3rd level:
l l stable
t bl with
ith 8
• Atoms are stable &
unreactive
i when
h the
h
outermost level is “full”
• Is the
h oxygen atom to the
h
right stable?
C)) How many
y pprotons?
4 (the atomic #)
D)) How many
y electrons?
4 (protons & electrons usually equal)
E) How many neutrons?
5
(9 protons & neutrons – 4 protons = 5 neutrons)
• Molecule: 2 or more atoms held
together by a covalent bond
– Form when atoms are unstable
(outer electron level not full)
• Covalent Bond: Chemical bond
where atoms share electrons
– Ex: Oxygen atom
– Only 6 electrons in outer
energy level
l l (unstable)
(
bl )
– 1 oxygen atom will share two
electrons
l t
with
ith another
th oxygen
– Therefore, both will have 8
electrons in its outer level (O2
is created)
e
e
e
ee
Cl atomic number = 17
Before the bondingg
After the bond
ee
ee
e
ee
e
e
e
Na atomic number = 11
ee
ee
e ee
e
e
ee
ee
• IIonic
i bbond:
d chemical
h i l bond
b d where
h electrons
l
are
gained/lost
• Held
ld together
h by
b magnetic
i attraction
i
• Cause: 1 atom may steal an electron from another
• Ion: + or – charged atom
• Ex: Sodium + Chlorine = Sodium Chloride
Quick Review
Q
• Atoms become stable when their outer
electron
l t
level
l l is
i “full”
“f ll”
• Molecules created when 2 or more atoms
combine together
• Covalent Molecules: share electrons
• Ions: lose and gain electrons
Na
Cl
Na
Cl
Protons
(+)
11+
17+
Protons
(+)
11+
17+
Electrons
(-)
11-
17-
Electrons
(-)
10-
18-
Net
charge
0
0
Net
charge
+1
-1

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