Transcript CHAPTER 2 - CHEMISTRY

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 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
 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
Atomic
Mass
 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
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
1st level – 2 electrons
2nd level – up to 8 electrons
3rd, 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 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
 Ex. Hydrogen gas (H2) - 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 “-”
 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)