Chapter 4 The Chemical Basis of Life

Matter Matter = any material substance with Mass & Volume

Matter Solid Liquid Gas comes in 3 phases

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 H= Hydrogen C= Carbon O= Oxygen N= Nitrogen S= Sulfur Na= Sodium Ca= Calcium K= Potassium I= Iodine Cl= Chlorine 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 Electrons - e - negative charge, orbiting nucleus Neutrons n 0 – no charge, in nucleus

Carbon Atom C Atomic Mass Atomic # minus Atomic # = # of n 0 = # of p + and # of e - Carbon has 6 p + and 6 e - Carbon has 6 n 0

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

Bohr Diagram and Lewis Structure

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

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; Nitrogen XXX X XX X N 7 14 ATOMIC STRUCTURE: Bohr Diagram 7P+ 7n0

Bohr Diagrams Draw the Bohr Diagram for the following elements: OCl a)b) 8p+ 8n0 X X X X X X X X 17p+ 18n0 X X X XX X XX X X X X X XX XX

Draw the Bohr Diagram for the following elements: Bohr Diagrams BNe c)d) 5p+ 6n0 X X X X X 10p+ 10n0 X X X X XX X 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

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

2p2n 10p10n 18p22n He Ne Ar ,8 2,8,8 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.

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

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

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

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

Sodium atom Na Sodium ion (Na + ) Chlorine atom Cl Chlorine ion (Cl - ) The Ionic Bond 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 Cl 2 Molecules have no overall electric charge Forces (bonds) between atoms in the molecule are very strong Each outer shell has 8 electrons Electrons shared

Cl Chlorine Cl 2 Cl Covalent bonds can be represented in 3 ways:

Oxygen O 16 8 Oxygen atom 2,6

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