The Chemical Basis of Life Chapter 4 The Chemical Basis of Life

Matter Matter = any material substance with Mass & Volume

Matter comes in 3 phases Liquid Solid Gas

Solid Definite Shape Definite Volume

Liquid Indefinite Shape – takes the shape of the container Definite Volume

Gas Indefinite Shape – takes the shape of the container Indefinite Volume – can expand and be compressed

Elements Pure substance that can not be broken down into other substances by chemical means

Examples of Elements C = Carbon Na = Sodium O = Oxygen Ca = Calcium K = Potassium H = Hydrogen I = Iodine N = Nitrogen Cl = Chlorine S = Sulfur P = Phosphorus

4 elements make up 96% of all living matter Hydrogen (H) Oxygen (O) Nitrogen (N) Carbon (C)

Most of remaining 4% is made of: Calcium (Ca), phosphorus (P), potassium (K), sulfur (S) Trace elements Make up less than 0.01 % of body mass Essential to life

Atom the smallest particle making up elements

Sub-atomic Particles Protons p+ - positive charge, in nucleus Neutrons n0 – no charge, in nucleus Electrons - e- negative charge, orbiting nucleus

C Carbon Atom 6 12.011 Atomic # = # of p+ and # of e- Carbon has 6 p+ and 6 e- Atomic Mass minus Atomic # = # of n0 Carbon has 6 n0

Drawing an Atom of Carbon e- e- 6 p+ 6 n0

HELIUM ATOM + - + - Shell proton neutron electron What do these particles consist of?

Compounds Substance containing two or more elements combined in a fixed ratio Properties are usually much different than those of the elements they contain Ex: H2O – liquid at room temperature, while hydrogen and oxygen are both gases Ex: NaCl – white crystal (table salt), while sodium is a silver-gray metal and chlorine is a yellowish-green gas

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Most isotopes are stable—their nuclei do not change over time

Radioactive Isotope Other isotopes contain nuclei that will change or decay over time Unstable isotopes Nucleus changes giving off radiation May be harmful Can be useful in research and/or medical diagnosis and treatment

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Bohr Diagram and Lewis Structure

Bigger energy level = higher energy ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shell a maximum of 2 electrons second shell a maximum of 8 electrons third shell a maximum of 8 electrons Bigger energy level = higher energy

ATOMIC STRUCTURE: Bohr Diagram With the Bohr Diagram (Dot & Cross diagrams) elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X Nitrogen N 7 X X 7P+ 7n0 X X 14 X X

Bohr Diagrams O Cl Draw the Bohr Diagram for the following elements: X 8 17 O Cl a) b) 35 X X 16 X X X X X 17p+ 18n0 X X X X X X 8p+ 8n0 X X X X X X X X X X

Bohr Diagrams B Ne Draw the Bohr Diagram for the following elements: X 5 10 B Ne c) d) 20 X X 11 X X X X 10p+ 10n0 X X X X X X 5p+ 6n0 X X X

Valence Electrons The electrons on the outermost energy level These electrons determine the element’s chemical properties and its ability to form chemical bonds.

Lewis Structure of Atom The chemical symbol for the atom is surrounded by a number of dots corresponding to the number of valence electrons. Examples Hydrogen atom has 1 valence electron H Fluorine atom has 7 valence electrons F

Lewis Structure Draw the Lewis Structure for the following elements: a) Li b) Cl c) P d) Mg

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Chemical Bonding Ionic and Covalent

Chemical Bonds Atoms react with one another to fill their outer energy levels Transferring or sharing electrons creates an attraction (chemical bond) that holds atoms together

Noble Gases Helium, neon and argon are atoms which do not react with other atoms. We call them “Noble Gases” because of this. Each of these gases has a full outer electron shell. 10p10n 18p22n 2p2n 2 Ne 10 He 20 4 Ar 18 40 2,8 2,8,8

IONIC BONDS Ionic bond: one atom transfers an electron to another atom Oppositely charged ions are attracted to one another forming a chemical bond  an ionic bond

Sodium 11 Na 23 e.c. 2,8,1 11p 12n 11 protons 12 neutrons 11 electrons

Chlorine Cl e.c. 2,8,7 17 protons 18 Neutrons 17 electrons 17 35 17p

+ The Sodium atom has 1 Electron in it’s outer shell. Na e.c. 2,8,1 Atom + The Sodium loses 1 electron to leave a complete outer shell. It is now a Sodium ion with a charge of 1 + (Na +) e.c. (2,8)+ Ion

- The Chlorine atom has 7 electrons in it’s outer shell. Cl e.c. 2,8,7 Atom - (Cl - ) The Chlorine gains 1 electron to gain a complete outer shell. It is now a Chlorine ion with a charge of 1 - e.c. (2,8,8)- Ion

The Ionic Bond + - Sodium atom Na Chlorine atom Cl Sodium ion (Na +) Chlorine ion (Cl -) The sodium atom loses one electron to attain a complete outer shell and become a positive ion (Na +). The Chlorine atom gains one electron to attain a complete outer shell and become a negative ion (Cl –). Strong forces attract the sodium and chlorine ions.

Covalent Bond Formed when atoms share electrons Electrons may be shared equally or unequally Molecule: two or more atoms held together by covalent bonds

Chlorine atom 2,8,7

2 Chlorine atoms Outer shells only

Chlorine molecule Cl2 Electrons shared Each outer shell has 8 electrons Forces (bonds) between atoms in the molecule are very strong Molecules have no overall electric charge

Covalent bonds can be represented in 3 ways: Chlorine Cl2 Cl Cl Cl Cl

Oxygen O 16 8 Oxygen atom 2,6

2 Oxygen atoms (outer shells only) Double covalent bond O

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LIFE DEPENDS ON THE UNIQUE PROPERTIES OF WATER

Water Molecule Water is a polar molecule Electrons are not shared equally between hydrogen and oxygen Electrons attracted to oxygen more strongly than to hydrogen Note: Hydrogen atoms in the water molecule are slightly positive and the oxygen atom slightly negative

WATER’S LIFE-SUPPORTING PROPERTIES Polarity of water and effects of hydrogen bonding give water its unique properties: Cohesion and adhesion Temperature moderation Low density of ice compared to water Ability to dissolve substances

COHESION & ADHESION Cohesion: an attraction between like molecules Adhesion: an attraction between unlike molecules Keep large molecules organized so they function properly in cells Help transport water through roots and leaves in plants

TEMPERATURE MODERATION Hydrogen bonds in water molecules allow water temperatures to change more slowly Through evaporation (sweating), water moderates temperature  absorbs heat energy from skin cooling the body

LOW DENSITY OF ICE Density: amount of matter/given volume For most substances, solids are more dense than liquid state of matter Due to hydrogen bonding, water is the opposite Liquid water is more dense than solid water Since less dense substances float in more dense substances, ice floats

WATER DISSOLVES OTHER SUBSTANCES Solution: uniform mixture of two or more substances Solvent: the substance that dissolves the other substance; present in the greater amount Solute: the substance that is dissolved; present in the lesser amount Aqueous solution: solution where water is the solvent

ACIDS, BASES, & pH Acid: Base: produce H+ ions in water pH less than 7 sour taste Base: removes H+ ions in water pH greater than 7 bitter taste pH scale: range of numbers that describes how acidic or how basic a solution is pH of 7 is neutral Buffers: substances that cause a solution to resist changes in pH