Transcript Atom

What is an Atom?
• Atom: Smallest unit of
all matter
• 3 Main Parts:
– 1) Proton (+ charge)
– 2) Neutron (No charge)
– 3) Electron (- charge)
• Protons & Electrons
usually equal in number
• Elements (substance
made of only 1 type of
atom) are identified on
the Periodic Table
(page R36)
Reading the Periodic Table
• Atomic Number: Number • How many protons,
of protons (+) the atom
electrons, and neutrons
contains
does Carbon contain?
– Usually # of electrons also
• Atomic Mass: Combined
# of protons and neutrons
inside the nucleus
– Electrons too small to affect
mass
Protons = ______
Electrons = ______
Neutrons = ______
What’s the:
A) Atomic number of
Beryllium?
4
B) Atomic mass of Beryllium?
9
C) How many protons?
4 (the atomic #)
D) How many electrons?
4 (protons & electrons usually equal)
E) How many neutrons?
5
(4 protons + ? neutrons = 9)
• Electrons orbit the nucleus
in “energy levels”
1st level:
• closest to nucleus
• stable w/ 2 electrons
2nd level:
• stable w/ 8 electrons
3rd level:
• stable w/ 8 electrons
• Atoms are stable when the
outermost level is “full”
Examine Carbon below. It
has 2 electrons in the first
level and 4 electrons in the
2nd level. Is Carbon stable?
• Molecule: 2 or more atoms held
together by a covalent bond
– Form when atoms are unstable
• Covalent Bond: Chemical bond
where atoms share electrons
– Ex: Oxygen atom
• Why unstable? Only 6
electrons in outer energy level
• What happens? Each oxygen
atom will share two electrons
with the other oxygen
• End result? Both will have 8
electrons in its outer level (O2 is
created)
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chlorine
sodium
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• Ionic bond: chemical bond where electrons are
gained/lost
– Creates Ions (atoms with + or – charge)
• Held together by magnetic attraction
• Cause: 1 atom steals an electron(s) from another atom
• Ex: Sodium + Chlorine = Sodium Chloride
Na atomic number = 11
Cl atomic number = 17
Before the bonding
After the bond
Na
Protons
(+)
Electrons
(-)
Net
charge
11+
110
Cl
Na
Cl
17+
Protons
(+)
11+
17+
17-
Electrons
(-)
10-
18-
0
Net
charge
+1
-1
Quick Review
• Atoms become stable when their outer
electron level is “full”
• Molecules created when 2 or more atoms
combine together
• Covalent Molecules: share electrons
• Ions: lose and gain electrons