ESCS Review
Composition of Matter (Review)
• Matter – anything that takes up space and has mass.
• Mass – the quantity of matter an object has (the same
as weight on Earth).
• Element – substances that cannot be broken down
chemically into simpler kinds of matter.
• Atom – the simplest part of an element that retains all
the properties of that element (tiny in size; would take 1
million to fill up the space of a period.)
• Nucleus – central region and the bulk of the mass of an
atom.
Atoms and Elements
3 parts of an atom
• Protons – positively charged subatomic particle, part of
the nucleus.
• Neutron – subatomic particle with no charge, other part
of the nucleus.
• Electron – negatively charged subatomic particle, found
outside the nucleus.
Elements on the periodic table
• Atomic number – the number of protons an atom has.
• Mass number – number of protons + neutrons.
Atoms and Elements
(continued)
Atoms with different numbers of
electrons or neutrons
• Ion – an atom or molecule with an electrical charge
because of the gain (makes – ion) or loss (makes + ion)
of an electron
– Ex. Na+ and Cl-
• Isotopes – atoms of the same element, that have a
different number of neutrons (would have the same
atomic number but different mass number.)
– Ex. Carbon-12, Carbon-13, and Carbon-14
• How many neutrons would each of these have?
• Are there any beneficial uses for isotopes?
Electrons determine the properties of
atoms
• Electrons determine the chemical properties of an atom
– The farther from the nucleus, the greater its energy.
– Occur at only certain energy levels (electron shells)
– Those electrons in the outer shell are the ones that are involved
in chemical bonds. They are called Valence Electrons.
Valence electrons
• The outer shell of an element can contain up to 8 valence electrons.
– All elements want to reach this number. This is when they have they are the
most stable (have the least amount of energy).
– The closer an element is to having 8 valence electrons, the more it wants to
receive this electron. This is called Electronegativity.
– As you travel to the TO THE RIGHT (because the 2nd last column has 7 electron)
and UP the periodic table, you become more electronegative
Molecules vs Compounds
(Review)
• Molecule – 2 or more atoms joined together. Ex. O2
• Compounds – a molecule that is made up of atoms
from two or more different elements. Ex. H20 or NaCl
Chemical Bonds – the attractive forces that hold
atoms together in molecules / compounds.
3 types of chemical bonds
(1) Covalent Bond – forms when two atoms share one or
more pairs of electrons. Can have single bond (share 2
electrons), double bond (share 4 electrons), or triple bond
(share 6 electrons)
2 types
• Polar covalent bond - Unequal sharing of electrons when
one of the atoms in the bond is more electronegative than the
other. This creates a partially positive “pole” and a partially
negative “pole”. Ex: H2O
• Nonpolar covalent bond – Equal sharing of electrons
between two atoms that are identical. Ex. O2
Chemical Bonds Continued
(2) Ionic Bond – forms when electrons are transferred
from one atom to another (when one atom is MUCH
MORE electronegative than the other). The resulting
positive and negative charges cause them to be
attracted to each other (bonding).
• Ex. Na+ + Cl - = NaCl
Chemical Bonds Continued
– (3) Hydrogen Bond – very weak bond between partially positive
hydrogen of 1 covalently bonded compound and a partially
negative atom of another covalently bonded compound.
• 1 of these bonds is very weak, but many of them together are strong
• Responsible for holding water together
Energy (Review)
• Energy – the ability to do work.
• Chemical reaction – one or more
substances change to produce one or
more different substances. Energy is
absorbed or released.
• Reactants – substances you start with in
a reaction (left of the arrow).
• Products – substances you end up with
after a reaction (right of the arrow).
• Activation energy – energy required to
start a reaction.
Balancing Chemical Formulas
• _ H2 + _O2
_ H20
• _CH4 + _O2
_CO2 + _H20
Solutions (Review)
• Solution – mixture where one substance
is uniformly distributed (dissolved) in
another.
• Solute – the substance that is dissolved.
• Solvent – the substance in which the
solute is dissolved.
• Concentration – the amount of solute in a
solvent.