The Chemistry of Life Chapter 2

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The Chemistry of LifeChapter 2
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Pre Assessment

1. Name the 3 parts of an atom and their locations
   in an atom
2. What subatomic particle represents an atoms
   atomic mass?
3. What units are used to measure the an atoms
   mass?
4. What is the maximum number of electrons in an
   atoms outer shell?

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Why are we studying chemistry?

• Chemistry is the foundation of Biology

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• Everything is made of matter
• Matter is made of atoms

Hydrogen 1 proton 1 electron
Oxygen 8 protons 8 neutrons 8 electrons
Proton
Neutron
Electron

0

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The World of Elements
H
C
O
N
P
S
Na
Mg
K
Ca
Different kinds of atoms elements
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Element

• A substance that cannot be broken down to other
  substances by ordinary chemical means.
• Composed of only one kind of atom
• 92 naturally occurring

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Atomic Number

• Number of protons (equals number of electrons)
• Examples
• Carbon 6
• Calcium 20

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Mass Number

• Equal to the sum of its protons and neutrons
• Example
• Sodium atomic number 11
• mass number 23
• How many protons, neutrons and electrons?
• Isotopesatoms of the same element that differ in
  the number of neutrons for example carbon-12 and
  carbon-14.

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Life requires 25 chemical elements

• About 25 elements are essential for life
• Four elements make up 96 of living matter
• carbon (C) hydrogen (H)
• oxygen (O) nitrogen (N)
• Four elements make up most of remaining 4
• phosphorus (P) calcium (Ca)
• sulfur (S) potassium (K)

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Table 2.1 Naturally Occurring Elements in the
Human Body
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Figure 2.5 Two simplified models of a helium
(He) atom
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Figure 2.9 Energy levels of an atoms electrons
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Figure 2.10 Electron configurations of the first
18 elements
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Check Point

• What happens to energy as electrons move away
  from the nucleus?
• What happens to energy as electrons move towards
  the nucleus?

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Figure 2.11 Electron orbitals
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Bonding properties

• Effect of electrons
• electrons determine chemical behavior of atom
• depends on numberof electrons in atoms
  outermost shell
• valence shell

How does this atom behave?
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Whats themagic number?
Bonding properties

• Effect of electrons
• chemical behavior of an atom depends on number of
  electrons in its valence shell

How does this atom behave?
How does this atom behave?
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Elements their valence shells
Elements in the same row have the same number of
shells
Moving from left to right, each element has a
sequential addition of electrons ( protons)
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Elements their valence shells
Elements in the same column have the same valence
similar chemical properties
Remember some food chainsare built on reducing
O to H2O some on reducing S to H2S
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Check Point

• How many valence electrons are in Carbon?
• How many valence electrons are in Phosphorus?
• How many valence electrons are in Potassium?
• How many shells are in Carbon?
• How many shells are in Phosphorus?
• How many shells are in Potassium?

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Check Point

• How many valence electrons are in Carbon?
• 4
• How many valence electrons are in Phosporus? 5
• How many valence electrons are in Potassium? 1
• How many shells are in Carbon? 2
• How many shells are in Phosporus? 3
• How many shells are in Potassium? 4

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Chemical reactivity Chem bond animation

• Atoms tend to
• complete a partially filled valence shell
• or
• empty a partially filled valence shell

This tendency drives chemical reactions
and creates bonds
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Bonds in Biology
Hydrogen bond
H2O

• Weak bonds
• hydrogen bonds
• attraction between and
• hydrophobic hydrophilic interactions
• interaction with H2O
• van derWaals forces
• (ionic)
• Strong bonds
• covalent bonds

H2O
Covalent bond
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Figure 2.14 Electron transfer and ionic bonding
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Figure 2.15 A sodium chloride crystal
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Covalent bonds

• Why are covalent bonds strong bonds?
• two atoms share a pair of electrons
• both atoms holding onto the electrons
• very stable
• Forms molecules

H H
H2 (hydrogen gas)
H2O (water)
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Multiple covalent bonds

• 2 atoms can share gt1 pair of electrons
• double bonds
• 2 pairs of electrons
• triple bonds
• 3 pairs of electrons
• Very strong bonds

More isbetter!
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Nonpolar covalent bond

• Pair of electrons shared equally by 2 atoms
• example hydrocarbons CxHx
• methane (CH4 )

balanced, stable,good building block
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Polar covalent bonds

• Pair of electrons shared unequally by 2 atoms
• example water H2O
• oxygen has stronger attraction for the
  electrons than hydrogen
• oxygen has higher electronegativity
• water is a polar molecule
• vs poles
• leads to many interesting properties of water

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Figure 2.12 Covalent bonding in four molecules
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Hydrogen bonding

• Polar water creates molecular attractions
• attraction between positive H in one H2O molecule
  to negative O in another H2O
• also can occur wherever an -OH exists in a
  larger molecule
• Weak bond
• Bond animation

H
H
O
Thats Weak
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Figure 2.13 Polar covalent bonds in a water
molecule
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Figure 2.16 A hydrogen bond
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Figure 2.17 Molecular shapes due to hybrid
orbitals
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Figure 2.19 A molecular mimic
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Chemical reaction between hydrogen and oxygen
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Figure 4.4 Variations in carbon skeletons
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Review

1. Which type of bond donates one electron from an
   atom to another?
2. When an atom loses an electron, what is it
   called?
3. When an atom gains an electron, what is it
   called?

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Review

1. Ionic bonds donate electrons opposite charges
   attract
2. Cation positively charged atom
3. Anion negatively charged atom

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Post Assessment

1. What is a trace element?
2. What is the maximum number of electrons in the 1s
   orbital?
3. What types of bonds form when 2 atoms are equally
   electronegative?
4. Provide an example of a compound.