Atoms

1
Atoms
2
What is the nature of matter?

• Salt can be divided into piles.
• Is there a point where salt can not be split any
  further?

3
Sowhat is an Atom?

• From Greek word atomos meaning unable to cut
• Atom basic unit of matter

Thats pretty small!
diameter 1 pm (picometer) 10 -12
4
A Brief History

• Democritus (4th Century BC)
• First named the atom
• Lacked evidence
• John Dalton (1766-1844)
• Performed experiments to discover
• Daltons Atomic Theory

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Daltons Atomic Theory
Um, who is this? He looks pretty different from
you and me, Carbon.
Im Oxygen. I am different from you, but Im
sure we could find some way to bond!
It sure is nice hanging out with you, Carbon.

1. All elements composed of tiny indivisible
   particles called atoms.
2. Atoms of the same element are identical

Tell me about it, Carbon!
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Still more of Daltons Atomic Theory

• Atoms of different elements can physically mix
  together or can chemically combine to form
  compounds.
• Chemical reactions occur when
• atoms are separated, joined or rearranged
• however, they are never changed into atoms of
  another element.

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Reflecting on Daltons Theory

• Most of Daltons theory is still accepted.
  Which part do you think has been rejected?

The Atom is Divisible!
Return to Theory 1 and cross out the word
indivisible
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The three kinds of subatomic particles

• 1. Protons (p)
• One unit of positive charge
• Relative mass 1 AMU
• Actual mass 1.67 x 10-24 grams
• - Found in the nucleus of the atom
• 2. Neutrons (n0)
• No charge
• Relative mass 1 AMU
• Actual mass 1.67 x 10-24 grams
• Found in the nucleus of the atom

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The three kinds of subatomic particles

• 3. Electrons (e-)
• Negative charge
• Relative mass 1/1836 AMU
• Actual mass 9.11 x 10-28 grams
• Found in the orbitals outside the nucleus

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In 1911, Rutherford performed an experiment

What did this prove?
Source of alpha particles
Thin sheet of gold foil
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Atoms are mostly empty space

• Rutherford proposed that the atomic structure was
  like planets around the sun
• This did not account for very specific traits
  that atoms possessed.

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Atomic Structure

• Protons and Neutrons make up the nucleus
• Electrons spin around in orbitals surrounding
  the nucleus

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• What makes atoms different from each other, if
  they have the same basic parts?

The Atomic Number
Definition The number of protons in the nucleus
of an atom, which also identifies the element
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Mass Number

• The total number of protons and neutrons is
  called the mass number.

Based on this nucleus, what is the mass
number? What element is it?
4

Helium

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Atomic Number vs. Mass Number

• The atomic number the number of protons
• Usually the of p of e-

• The Mass Number the total of p and no
• The mass number is here.

• 2
• He
• 4. 00
• Helium

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Why protons?Why not neutrons?Or electrons?

• Oxygens Atomic Number is 8.
• How many protons does it have? _______
• How many neutrons does it have? ________
• How many electrons does it have? ________

8
8
8
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Electron Orbitals

• The 1st orbital of an atom (closest to the
  nucleus) can hold 2 electrons
• The 2nd orbital of an atom can hold up to 8
  electrons octet rule

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The Atomic Number
B
5
5
P _____
6
N _____
Elements Name
Boron
5
E _____
Atomic Mass
10.81
Bohr Diagram
Lewis Structure
B
Valence Number 3
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Bonding and Chemical Reactions
Hi there! Im Nitrogen. Am I an atom or a
compound?
You were right! I am now Ammonia! But, am I an
atom or a compound now?
Greetings, Nitrogen. We are Hydrogen atoms.
Perhaps we will change the way you think about
yourself.

• Chemical Bonding
• Combining Atoms of Elements to form Chemical
  Compounds

Oh, you cant be serious!
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Chemical Symbols of Elements

• 1st Letter of Symbols are Capitalized
• Ex. C Carbon S Sulfur
• Ca Calcium Si Silicon

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Bonding

• An atom is most stable when its outer orbital is
  either full or empty
• To do this, it will either gain, lose or share
  electrons.

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Ionic BondingA bond that involves a transfer of
electron
Ex. Sodium Chloride (NaCl) Salt!
Cl -1 ion
Na1 ion

• Sodium Chlorine

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What keeps ionic bonds together?

• One atom loses its electron, therefore becoming a
  positive () ion.
• The other atom gains an electron, therefore
  becoming negative (-) ion.
• Opposites attract!

Luv ya too! (-)
Luv ya honey! ()
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Covalent Bonds
Can you guess which element I am?
What will complete my valence shell?

• A covalent bond is a chemical bond formed by
  sharing electrons.

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Different types of Covalent Bonds

• Single Bond One pair of shared electrons
• Double Bond Two pairs of shared electrons
• Triple Bond Three pairs of shared electrons
• Hydrogen Cyanide (HCN) can form this.
• Can you?

H H
H
H
C
O
OCO
O
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Bonding Basics Practice
1-
1-
2

• Ionic Bonds
• Mg Br
• Pb S
• Al Cl

Mg
Br
Br
MgBr2
4
2-
2-
Pb
S
S
PbS2
1-
Cl
Cl
Al
Cl
AlCl3
3
1-
1-
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Bonding Basics Practice

• Covalent Bonds
• H Cl
• C Cl
• Si O

H
Cl
H Cl
HCl
Cl
Cl
CCl4
C
Cl
Cl
C
Cl
Cl
Cl
Cl
Si
O
O Si O
SiO2
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How do you count atoms?

• Subscript of atoms within that molecule
• 2 Hydrogen
• 1 Oxygen

H2O
3Al2(SO4)3
Al2(SO4)3
Number in front indicates of entire molecular
unit 6 Aluminum 9 Sulfur 36 Oxygen
Subscript multiple of everything within the
parenthesis 2 Aluminum 3 Sulfur 12 Oxygen
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Chemical Equations

• Chemical equations are sentences that describe
  chemical reactions
• A chemical reaction involves the breaking and
  reforming of chemical bonds (rearrangement of
  atoms)
• Reactants (ingredients) ? Products (whats made)
• 2 H2 O2 ? 2 H2O

?
Equations are balanced same number of atoms
on both sides of the arrow.