Chemistry: Composition of Matter

Matter Anything that occupies space and mass Mass: amount of matter in an object Mass ≠ Weight Chemical changes are essential to all life Non-living substance  living substances

Elements Pure substances that cannot be broken down chemically into simpler kinds of matter 100+ identified Less than 30 important to living things IMPORTANT ELEMENTS: CHON –Carbon –Hydrogen –Oxygen –Nitrogen

Symbol: consist of one or two letters Atomic number: number of protons Atomic mass: sum of protons and neutrons in nucleus

Atoms Simplest particle of an element that retains all of the properties of the element So small, structures cannot be observed Scientists created models Models: –NOT meant to show how atom looks –Help understand structure of atom –Predict how atom will act

Atomic Structure Nucleus Electrons

Nucleus Central core Two kinds of particles: –Proton: POSITIVE electrical charge –Neutron: NO electrical charge

Electrons HIGH ENERGY particles with very little mass move around nucleus at very high speeds in one of several different energy levels

Energy Levels Outer levels have MORE energy than inner levels First energy level can only hold TWO electrons Second energy level can hold up to EIGHT electrons

Atomic Number Number of protons Proton number same in ALL atoms of same element Protons=Electrons Positive=Negative=Neutral

Compounds Pure substance made up of atoms of two or more elements Naturally elements do NOT exist by themselves

Chemical Formulas Show kind and proportion of atoms of each element in compound Ex: H 2 O

Physical and chemical properties of COMPOUNDS differ from individual ELEMENTS Atom is most stable when outermost energy level is filled Most atoms NOT stable in natural state so they make compounds

Chemical Reactions Typically unstable elements combine in ways that cause their atoms to become stable Types: –Covalent –Ionic Process: 1.chemical bond broken 2.Atoms rearranged 3.New chemical bonds (attachments) formed

Covalent Bonds Forms when two atoms share one or more pairs of electrons Molecule: simplest part of a substance that retains all the properties of that substance

Ionic Bonds Ion: an atom or molecule with an electrical charge ( + or - ) When two oppositely charge atoms combine and one electrons is transferred

Energy

Energy and Matter Energy: the ability to do work or cause change Amount of energy in universe remains the same Energy changes in form Flow of energy from sun to living things is the chemistry of living things

Energy in Living Things Important forms of energy: –chemical energy –thermal energy –electrical energy –mechanical energy Free Energy: the energy is a system that is available for work Breakfast  thermal, mechanical energy

States of Matter All atoms of any substance are in constant motion Rate of atoms or molecules motion determine state of substance Types of state: –Solid –Liquid –Gas

Solid Particles – tightly linked together –in definite shape –vibrate in place Maintains fixed volume and shape

Liquid Particles –Not as tightly linked as a solid –Move more freely than a solid  FLOW Flow to conform to shape of container Maintain fixed volume

Gas Particles –move most freely and RAPIDLY –little to no attraction to each other Fill volume of container they occupy

Changing State of Matter THERMAL ENERGY must be added to substance

Energy and Chemical Reactions Living things undergo thousands of chemical reactions VERY complex (interrelated and multistep) Reactants: what you start with, the LEFT side of equation Products: what you end with the RIGHT side of equation

Energy Transfer Main energy supply of body : SUGAR Chemical Reactions: Sugars  CO 2 + H 2 O Types: –Exergonic Reaction: release free energy –Endergonic Reaction: absorbs free energy

Activation Energy Amount of energy needed to start reaction Catalyst: reduce the amount of activation energy needed Enzyme: important class of catalysts in living things Single organisms may have thousands of different kind

Reduction-Oxidation Reactions Redox reactions: Electrons transferred between atoms Oxidations reaction: reactant lose 1+ electrons; results in positive charge Reduction reaction: reactant gains 1+ electron; results in negative charge Electron given up by one substance and accepted by another

Solutions

Why? Most mass of living things is WATER Chemical reactions of life occur mostly in water solutions Electricity of nerves transmits through watery pathways of dissolved ions Chemical messengers move through watery medium of body

Solution A mixture in which one or more substances are uniformly distributed in another substance Can be: –liquid –solid –gas

Parts of a Solution Solute: substance dissolved in solution Solvent: substance in which the solute is dissolved Saturated solution: no more solute can be dissolved

Aqueous Solution Water is solvent VERY important to living things Marine microorganisms, plant nutrients, cells

Dissociation of Water Force of attraction between atoms so strong, oxygen atoms steals hydrogen atom from another water molecule Water molecule  2 ions with opposite charges hydronium hydroixde ion ion

Acid Hydronium ions > Hydroxide ions Sour tasting

Base Hydroxide ions > Hydronium ions Bitter tasting Feel slippery

pH scale Scale to compare relative concentration of hydronium ions and hydrogen ions in a solution

Buffers Enzymes can only function at certain pH levels Buffers: chemical substances that neutralize small amounts of acid or base