Week 2-2 Basic Chemistry

Chapter 02

Basic Chemistry

Basic Chemistry

Outline Chemical Elements  Atoms  Isotopes  Molecules and Compounds

Chemical Bonding  Ionic and Covalent  Hydrogen

Properties of Water Acids and Bases

Biosphere Ecosystem A community and its physical environment

Community The populations of all species occupying the same area

Population A group of individuals of the same kind (species) occupying a given area

Multicelled organism An individual composed of specialize, interdependent cells most often organized in tissues, organs, and organ systems

Organ system Two or more organs interacting chemically, physically, or both in ways that contribute to survival of the whole organism

Tissue An organized group of cells and surrounding substances functioning together in a specialized activity

Cell Smallest unit having the capacity to live and reproduce, independently or as part of a multicelled organism

Organelle Inside all cells except bacteria, a membrane-bound sac or compartment for a separate, specialized task

Molecule A unit in which two or more atoms of the same element or different ones are bonded together

Atom Smallest unit of an element (a fundamental substance) that still retains the properties of that element

Subatomic particle An electron, proton, or neutron; one of the three major particles of which atoms are composed

Living matters

Levels of biological organization

All those regions of Earh’s waters, crust, and atmosphere in which organisms can exist

Life and Chemistry: Small Molecules •

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Water and the Origin of Life’s Chemistry

Atoms: The Constituents of Matter

Chemical Bonds: Linking Atoms Together

Chemical Reactions: Atoms Change Partners

Water: Structure and Properties

Acids, Bases, and the pH Scale

Properties of Molecules

Water and the Origin of Life’s Chemistry • The earliest chemical signatures of life on Earth are about 4 billion years old. • The presence of water, possibly brought by comets striking the Earth, was critical in making conditions suitable for life. • Environmental conditions conducive to life evolved during the Hadean period.

Figure 2.1 A Geological Time Scale

Atoms: The Constituents of Matter

• All matter is composed of atoms.

• Each atom consists of at least one proton and one electron. • Atoms have mass. The mass comes mostly from the proton and a neutrally charged body called a neutron.

The Helium Atom

Atoms: The Constituents of Matter • Each element contains only one type of atom. • Information on elements is arranged in logical order in a table called the periodic table. • The periodic table arranges elements left to right based on their atomic number, and in columns based on similarities in their properties.

Figure 2.3 The Periodic Table (Part 1)

Figure 2.3 The Periodic Table (Part 2)

Atoms: The Constituents of Matter • Each element has a unique atomic number which is the number of protons found in an atom of the element. • The mass number is the number of protons plus the number of neutrons. • The mass number is used as the weight of the atom, in units called daltons. • Each element has a unique symbol: H is hydrogen, C is carbon, Na is sodium, and Fe is iron.

Atoms: The Constituents of Matter • All atoms of an element have the same number of protons, but not necessarily the same number of neutrons. • Atoms of the same element that have different atomic weights are called isotopes.

Figure 2.4 Isotopes Have Different Numbers of Neutrons

Bohr Models of Atoms

Atoms: The Constituents of Matter • Some isotopes are radioisotopes, which emit energy as alpha, beta, and gamma radiation from their nuclei. • Radioactive decay transforms the original atom into another atom, usually of another element.

Atoms: The Constituents of Matter • The region in which an electron travels is called the electron’s orbital. • The orbitals constitute a series of electron shells, or energy levels, around the nucleus. • Two electrons at most can occupy each orbital.

Atoms: The Constituents of Matter • The first shell is the innermost shell and has just one orbital, called the s orbital. • The s orbital fills first and its electrons have the lowest energy. • The second shell is next closest to the nucleus and has one s and three p orbitals. • The second shell can accommodate eight electrons, two per orbital.

Figure 2.6 Electron Orbitals

Atoms: The Constituents of Matter • The outermost shell of an atom determines how it reacts with other atoms. • Generally, if eight electrons are in the outer shell, the atom is stable and does not tend to react. • Atoms which do not have eight electrons in the outermost shell will share, gain, or lose electrons to arrive at a stable state.

Atoms: The Constituents of Matter • The tendency of atoms to be stable when they have eight electrons in their outermost shells is called the rule of eight, or the octet rule. • Hydrogen and phosphorus are exceptions to the octet rule.

Chemical Bonds: Linking Atoms Together • A molecule is two or more atoms bonded together. • A chemical bond is an attractive force that links two atoms together.

Chemical Bonds: Linking Atoms Together • A covalent bond is formed by sharing of a pair of electrons between two atoms. • In hydrogen molecules (H2), a pair of electrons share a common orbital and spend equal amounts of time around each of the two nuclei. • The nuclei stay some distance from each other due to mutually repelling positive charges.

Figure 2.8 Electrons Are Shared in Covalent Bonds

Properties of Molecules

Chemical Bonds: Linking Atoms Together • Molecules made up of more than one type of atoms are called compounds. • Every compound has a molecular weight that is the sum of all atoms in the molecule.

Chemical Bonds: Linking Atoms Together • Covalent bonds are very strong. • Each covalent bond has a predictable length, angle, and direction, which makes it possible to predict the three-dimensional structures of molecules. • A double covalent bond occurs when atoms share two pairs of electrons; in triple covalent bonds atoms share three electron pairs.

Figure 2.10 Covalent Bonding With Carbon

Properties of Molecules

Chemical foundations for Atom: the small particle retained the properties of an element Cells

• • An atom consists of proton(s), electron(s), and neutron(s)

Electron

Oxygen atom

Hydrogen atom H20

Proton

Animation: Atomic structure (Chapter 2-1, Figure 2).

29

Basic Chemistry

Atomic Structure Atoms - Smallest particles of elements Atoms composed of three types of subatomic particles  Protons

­ Positive charge ­ In nucleus

 Neutrons

­ Neutral charge ­ Also found in nucleus

 Electrons

­ Negatively charge ­ Orbit nucleus

Helium

Periodic Table (Revisited) Vertical columns indicate number of electrons in outermost shell VII I

I 1

Horizontal periods indicate total number of electron shells

1 2

H

2

1.008 3

I I

I V

V

4

II I

6

7

Li

Be

B

C

N

5

He

V I

VI I 9

4.003 10

O

F

Ne

8

6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18

3

Na Mg Al

Si

P

S

Cl

Ar

22.99 24.31 26.98 28.09 30.97 32.07 35.45 39.95 19 20 21 22 23 24 25 26

4

K

Ca Ga Ge As Se

Br

Kr

39.10 40.08 69.72 72.59 74.92 78.96 79.90 83.60

Basic Chemistry

Periodic Table Elements grouped in periodic table based on characteristics  Vertical columns = groups; chemically similar  Horizontal rows = periods; larger and larger I

VIII

1

Periods

1 H

1.008 3

II 4

2 Groups He III IV V VI VII 4.003 5

2 Li Be B

6

7

8

9

10

C

N

O

F

Ne

6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18

3 Na Mg Al Si

P

S

Cl

Ar

22.99 24.31 26.98 28.09 30.97 32.07 35.45 39.95 19 20 21 22 23 24 25 26

4 K Ca Ga Ge As Se Br Kr

39.10 40.08 69.72 72.59 74.92 78.96 79.90 83.60

Basic Chemistry

Chemical Elements Matter:  Refers to anything that has mass and occupies space  Only 92 naturally occurring fundamental types of matter – 92 Elements

Organisms composed primarily (98%) of only six elements  Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur  CHNOPS

Basic Chemistry

Elements and Compounds Molecule - Two or more atoms bonded together  If all atoms in molecule are of the same element ­ Material is still an element ­ O2, H2, N2, etc.

 If at least one atom is from a different element ­ Material formed is a compound ­ CO2, H2O, C6H12O6, etc. ­ Characteristics dramatically different from constituent elements

From Atoms to Molecules • Two or more atoms bond form a molecule Na Na+ Na­Cl NaCl Cl ClN­N N 2N

covalent bond

2

H+

ionic bond

H+

• Three kinds of bond:

C2+

N3­

– Ionic bond – Covalent bond – Hydrogen bond

Animation: CH4 ionic bond (Chapter 3-1, Figure 1), C2H6 covalent bond ( Figure 2),

35

Types of Bonds: Ionic Bonding

Basic Chemistry

Ionic Bonds

­ Atoms “want” 8 electrons in outer shell  If

have < 4 outers, desire to donate them  If have > 4 outers, desire to receive more

 Consider two elements from opposite ends of periodic table ­ Element from right side:  Has

7 electrons in outer shell  “Desperately wants” one more (7+1=8)

­ Element from left side:  Has

only 1 electron in outer shell  “Desperately wants” to donate it (1-1=0=8)

Types of Bonds: Ionic Bond Example

Basic Chemistry

Sodium:  From left end  Has 1 outer electron

Chlorine:  From right end of table  Has 7 outer electrons

In reaction, Na completely gives up its outer electron to Cl  Na now a positive ion and Cl a negative ion  Dissimilar charges now bind ions together  Forms sodium chloride ­ An ionic compound ­ NaCl table salt)

Formation of Sodium Chloride

Types of Bonds: Covalent Bonds

Basic Chemistry

When atoms are horizontally closer together in the periodic table  The electrons are not permanently transferred from one atom to the other like in NaCl  A pair of electrons from the outer shell will “time share” with one atom and then the other  This also causes the atoms to remain together  Known as covalent bonding

Sometimes two par of electrons are shared between atoms – a double covalent bond

Covalently Bonded Molecules

Types of Bonds: Hydrogen Bonds

Basic Chemistry

Water (H2O or H–O–H) is a polar molecule  Electrons spend more time with O than H’s  H’s become slightly +, O slightly –

When polar molecules are dissolved in water  The H’s of water molecules are attracted to the negative parts of the solute molecules  Results in a weak bond – the hydrogen bond  Easily broken, but many together can be quite strong

Water Molecule

Hydrogen Bonding

The Chemistry of Water: Heat Capacity

Basic Chemistry

Water has a high heat capacity  Temperature = rate of vibration of molecules  Apply heat to liquid ­ Molecules bounce faster ­ Increases temperature

 But, when heat applied to water ­ Hydrogen bonds restrain bouncing ­ Temperature rises more slowly per unit heat ­ Water at a given temp. has more heat than most liquids

Properties of Water: Heat of Vaporization

Basic Chemistry

High heat of vaporization  To raise water from 98 to 99 ºC; ~1 calorie  To raise water from 99 to 100 ºC; ~1 calorie  However, large numbers of hydrogen bonds must be broken to evaporate water  To raise water from 100 to 101 ºC; ~540 calories!

This is why sweating (and panting) cools  Evaporative cooling is best when humidity is low because evaporation occurs rapidly  Evaporative cooling works poorest when humidity is high because evaporation occurs slowly

Cooling of Animals

Basic Chemistry

Properties of Water: Water as a Solvent

Basic Chemistry

Solutions consist of:

 A solvent (the most abundant part) and  A solute (less abundant part) that is dissolved in the solvent

Ionic compounds dissociate in water  Na+

­ Attracted to negative (O) end of H2O ­ Each Na+ completely surrounded by H2O

 Cl-

­ Attracted to positive (H2) end of H2O ­ Each Cl- completely surrounded by H2O

Properties of Water: Heat of Fusion

Basic Chemistry

Heat of fusion (melting)  To raise ice from -2 to -1 ºC; ~1 calorie  To raise water from -1 to 0 ºC; ~1 calorie  To raise water from 0 to 1 ºC; ~80 calories!

This is why ice at 0 ºC keeps stuff cold MUCH longer than water at 1 ºC This is why ice is used for cooling  NOT because ice is cold  But because it absorbs so much heat before it will warm by one degree

at Various Temperatures

Basic Chemistry

Properties of Water: Uniqueness of Ice

Basic Chemistry

Frozen water less dense than liquid water  Otherwise, oceans and deep lakes would fill with ice from the bottom up  Ice acts as an insulator on top of a frozen body of water  Melting ice draws heat from the environment

Density of Water at Various Temperatures

A Pond in Winter

Water as a Transport Medium

pH of Water: Acids

Basic Chemistry

Acids  Dissociate in water and release hydrogen ions (H+)  Sour to taste  Hydrochloric acid (stomach acid) is a gas with symbol HCl ­ In water, it dissociates into H+ and Cl­ Dissociation of HCl is almost total, therefore it is a strong acid

pH of Water: Bases

Basic Chemistry

Bases:  Either take up hydrogen ions (H+) or release hydroxide ions (OH-)  Bitter to taste  Sodium hydroxide (drain cleaner) is a solid with symbol NaOH ­ In water, it dissociates into Na+ and OH­ Dissociation of NaOH is almost total, therefore it is a strong base

Basic Chemistry

pH Scale pH scale used to indicate acidity and alkalinity of a solution.  Values range from 0-14 ­ 0 to <7 = Acidic ­ 7 = Neutral ­ >7 to 14 = Basic (or alkaline)

 Logarithmic Scale ­ Each unit change in pH represents a change of 10X ­ pH of 4 is 10X as acidic as pH of 5 ­ pH of 10 is 100X more basic than pH of 8

The pH Scale

Basic Chemistry

Review Chemical Elements  Atoms  Isotopes  Molecules and Compounds

Chemical Bonding  Ionic and Covalent  Hydrogen

Properties of Water Acids and Bases

Ending Slide Chapter 02

Basic Chemistry