CHAPTER 2 - CHEMISTRY  2-1: Composition of Matter  2-2: Energy  2-3: Water + Solutions

2-1 : Composition of Matter  Matter – anything that has mass and takes up space  Mass – the quantity of matter an object has  Mass = Weight ~ WHY???? Weight involves the pull of gravity on an object

Elements element  An element is a pure substance that cannot be broken down chemically into simpler kinds of matter Over 100 elements have been identified 90% of all living things are made up of four: Carbon (C) Hydrogen (H) Oxygen (O) Nitrogen (N) Chemical symbols – 1 or 2 letters (uppercase/lowercase)

ATOMS atom.  The simplest particle of an element that retains all of the properties of that element is an atom. Too small to see but models can describe structures + properties  Atom’s “parts”: Nucleus – central core of an atom Protons – positively-charged particles (p + ) Neutrons – have no charge (n 0 )  Atomic #= # of protons in nucleus (and e - )  Atoms are neutral if the # protons (p + ) = # electrons (e - )  Isotopes – different # of neutrons Atomic Mass

ATOM’S (cont.)  Electrons (e - ) negatively-charged subatomic particles High energy particles with little mass Electrons can be found orbiting the nucleus of an atom in energy levels  1 st level – 2 electrons  2 nd level – up to 8 electrons  3 rd, 4 th, etc. – more than 8 electrons

What does an Atom look like?

Energy Levels Diagrams

Compounds  Under natural conditions, elements do not exist alone  Compound – a pure substance made up of 2 or more elements Chemical formula – tells # and kind of atoms in the compound  Ex. Water – H 2 O 2 Hydrogen atoms, 1 Oxygen atom  Chemical + physical properties of compounds differ than that of elements Ex. O 2 (gas) + H 2 (gas) = H 2 O (LIQUID) stable filled  If an atom is stable – its outer energy level is filled  Most atoms are unstable in natural state – tend to react/combine with other atoms to become stable - - known as a chemical reaction

Chemical Bonds  Bond – joining of atoms to create molecules or compounds  Chemical bonds are formed once rearrangement of atoms occurs – can happen all the time!!!!

Types of Bonds  Covalent Atoms share one or more pairs of electrons Ex. Water

More Covalent Bonding… Molecule – simplest part of a substance that retains all the properties of the substance and can exist in a free state DIATOMIC Ex. Hydrogen gas (H 2 ) - DIATOMIC

Bonds (cont.)  Ionic Atoms transfer electrons – creates an ion – carries an electrical charge Opposite electrical charges attract one another – this attraction is known as an ionic bond  “+” likes “-” ionic compound Resulting compound = ionic compound

Example: Sodium + Chlorine  By losing its outermost electron, an Na atom becomes an Na + ion  By gaining one electron, a Cl atom becomes a Cl - ion

Ionic compounds usually have an overall ZERO net charge, but may also have a slight charge to them Ex. Sodium ion + Chloride ion =  Na + + Cl - = Sodium Chloride (NaCl)