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Bi 183 HP

General Chemistry

Lecture 2

Fall 2011

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Terms we need to Know

Matter

Element

Atom

Atomic Structure

Atomic Nucleus

Proton

Neutron

Electron

Atomic Number

Atomic Mass

Isotope

Compound

Molecule

Chemical Bonds

Ionic

Covalent

Hydrogen

Chemical Reactions

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Nucleus

Cloud of negative

charge (2 electrons)

(a)

(b)

2 Protons

2 Neutrons

2 ElectronsHelium

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The number of neutrons and/or electrons can change.

Isotope = change the number of neutrons

Ion = electrically charged atom due to a change in the number of

electrons

cation = positive ion [lacking at least one electron]

anion = negative ion [gained at least one electron]

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What do Atoms look like????

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Atomic Structure: Where are the Electrons???

Electrons travel at various distances (Shells) around nucleus in zones called Orbitals

I

shell # orbitals Max # electrons

1 2

II

III

4

4

8

8

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Octet Rule (For most Atoms)

Outermost energy level (Shell) of an atom contains 4 orbitals.

Atom most stable when all 8 electrons present

Exception to Octet Rule

Energy level (Shell) nearest nucleus only contains 1 orbital.

Atom most stable when all 2 electrons present obviously this is helium

Valence ElectronsElectrons found in the outermost Shell of an atom

Atomic Structure:

Electrons determine if/how atom react with other atoms

Number ofValence electrons DETERMINES if/how Atoms react with each other

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Atomic Structure:

Valence Electrons determine if/how an atom react with other atoms

Which of these two elements is more reactive??

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Electron

First

electron shell(can hold2 electrons)

Outermost

electron shell(can hold8 electrons)

Carbon (C)Atomic number = 6

Nitrogen (N)Atomic number = 7

Oxygen (O)Atomic number = 8

Hydrogen (H)Atomic number = 1

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Chemical Bonds and Molecules

Molecular Formula

Contains chemical symbols of elements found in molecule

Subscript shows how many of each atom are present

ex. H2CO3

NaCl

Force holding Molecules together is a chemical bond

3 types of chemical bonds

1. Ionic bonds

2. Covalent bonds

3. Hydrogen bonds

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Formed by the attraction ofoppositely charged IONS

Cation bonds with an Anion

Strong But not as strong as Covalent bonds

Ionic Bondstransfer of electrons

Everyday

table saltNaCl Crystal

Cation Anion

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Formed when atoms share pair/s electrons

Key properties

Strong : strength increases with the number of shared

electrons

Verydirectional: They are formed between

two specific atoms

2 types:

Non Polar Covalent

Polar Covalent

Covalent Bonds

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Covalent Bonds

Water molecules contain 2 polar covalent bonds

Water is a polar molecule

Electronegativity

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Hydrogen Bonds

Hydrogen atom from one polar molecule

attracted to an electronegative atom

Individually weak bonds that can form and

break easily

Collectively they are strong bonds overall

ex. holds DNA strands together

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Chemical reactions make and

break chemical bonds

Chemical reactions are the making and breaking of

chemical bonds

The starting molecules of a chemical reaction are called

reactants

The final molecules of a chemical reaction are called

products

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Reactants Reaction Products

2 H2 O2 2 H2O

A Chemical Reaction

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Photosynthesis

Photosynthesis is an

important chemical reaction

Sunlight powers the

conversion of carbon dioxideand water to glucose and

oxygen

6 CO2 + 6 H20 C6H12O6 + 6 O2

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All chemical reactions are, in theory, reversible:products of the forward reaction becomereactants for the reverse reaction

Chemical equilibrium is reached when the forwardand reverse reaction rates are equal

We will spend more time on reactions when webegin our discussion of metabolism

Chemical Reactions