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 An elementelement 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 The simplest particle of an element that retains

all of the properties of that element is an atom.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 (n0)

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 particlesHigh energy particles with little massElectrons can be found orbiting the

nucleus of an atom in energy levels1st level – 2 electrons2nd level – up to 8 electrons3rd, 4th, 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 – H2O

2 Hydrogen atoms, 1 Oxygen atom

Chemical + physical properties of compounds differ than that of elements Ex. O2 (gas) + H2 (gas) = H2O (LIQUID)

If an atom is stablestable – its outer energy level is filledfilled

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

CovalentCovalent 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

Ex. Hydrogen gas (H2) - DIATOMICDIATOMIC

Bonds (cont.)

IonicIonic 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 “-”

Resulting compound = ionic compoundionic 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)