Chapter 4 Section 1 Notes
Matter
matter – anything that takes up space (has volume) and has mass
o
mass – amount of matter in an object
o
matter also has density (D=mass/volume)
o
matter also shows gravity
Properties of Matter
physical properties – characteristics that can be observed without changing the identity of the object
o
density
o
color
o
hardness (Mohs Hardness Scale)
o
freezing/melting point
o
boiling point
o
conductivity of electricity
chemical properties – characteristics that describe how a substance can react with other substances to produce new substances
o
iron reacting oxygen to form rust
o
burning of paper
physical change – any change to a substance that does not change the identity of the object
o
tearing
o
boiling/freezing/melting
chemical change – the ability of an object to change into a new substance
o
burning
o
forming rust
Elements
a substance that cannot be broken down into simpler substance through ordinary chemical means
each element has a characteristic set of properties
o
chemical
o
physical
more than 90 occur naturally
eight make up more than 98% of Earth’s crust (fig. 1 page 81)
Atoms
the smallest unit of an element that has the properties of that element
cannot be broken down into smaller particles and have the same properties
about 1 000 000 atoms stacked side to side will equal the thickness of a single piece of paper
Atomic Structure
subatomic particles – small particles that make up atoms
o
proton

positive charge

located in the nucleus

mass of 1 amu
o
neutron

neutral charge

located in the nucleus

mass of 1 amu
o
electron

negative charge

located in the electron cloud

no mass (1/1820 of a proton)
The Nucleus
small region in the center of the atom
o
proton
o
neutron
positive charge
makes up most of the mass of the atom
very little of the volume of the atom
an atom is mostly empty space
The Electron Cloud
region of space around the nucleus that holds electrons
the attraction of the electrons to the nucleus holds the electrons in place
Atomic Number
number of protons in the nucleus
all atoms of a given element have the same atomic number
sets the atoms apart from other atoms
atomic number is equal to the number of electrons of an electrically neutral atom
periodic table
o
a system (chart) for classifying elements
o
elements in the same column have similar arrangements of electrons
o
elements in the same column have similar properties

physical

chemical
Atomic Mass
mass number – sum of the number of protons and neutrons
expressed in atomic mass units (amu)
electrons add very little to the total mass, therefore, their mass is not calculated
Isotopes
atoms that have the same atomic number but have a different atomic mass
number of neutrons differ
different isotopes of the same element have slightly different properties
o
Hydrogen

Protium (1 proton, 0 neutrons)

Deuterium (1 proton, 1 neutron)

Tritium (1 proton, 2 neutrons)
Average Atomic Mass
the weighted average of the atomic masses of the naturally occurring isotopes of an element
weighted average of the atomic masses determine the average atomic mass
Valence Electrons and Periodic Properties
elements on the are arranged in columns based on similarities
groups – columns of the periodic table
determined by the number of valence electrons
o
valence electrons – outermost electrons of an atom
groups 1 and 2 have 1 and 2 valence electrons respectively
groups 13 – 18 have group number minus 10 valence electrons
groups 2 -1 2 have two or more valence electrons
o
metals – atoms that have 3 or fewer valence electrons
o
nonmetals – atoms that have 4 or more valence electrons
Chapter 4 Section 2 Notes
Combination of Atoms
compound – a substance made up of atoms of two or more different elements chemically combined
properties of a compound differ from those of the individual elements (NaCl)
Molecules
molecule – a group of atoms that are held together by chemical forces; a molecule is the smallest unit of matter that can exist by itself and retain all of a
substance’s chemical properties
diatomic molecules – made up of only two atoms of the same element
o
H2, O2, F2, I2, Br2, Cl2, N2
Chemical Formulas
elements occur in the same relative proportions
chemical formula – a combination of letters and number that show types and amounts of elements
water
o
H2O
o
Subscript

small number in front of an element

related to the preceding element

identifies how many of that element
o
two hydrogen atoms
o
one oxygen atom
Chemical Equations
a formula that describes a reaction
o
H2 + O2 → H2O
Equation Structure
reactants
o
elements/molecules on the left side of the equation
o
elements/molecules that react chemically
product
o
elements/molecules on the right side of the equation
o
elements/molecules that are produced by a chemical reaction
arrow (→)
o
separates the reactants from the products
o
means “gives”, “yields” or “produces”
Balanced Equations
equations must be balanced
equations are balanced when number and kinds of elements on the reactant side equal the number and kinds of elements on the product side
balancing
o
cannot change chemical formulas
o
use coefficients

number placed in from of an element/molecule

coefficient distributes to entire molecule
Chemical Bond
forces that hold the atom in a molecule together
form because the attraction between the positive and negative charges
form by the sharing or transferring of electrons
Ions
an atom or group of atoms that has a positive or negative charge caused by the losing or sharing of electrons
cation
o
positive ion
o
loses electrons
o
metals form cations
o
Na+1
anion
o
negative ion
o
gains electrons
o
nonmetals form anions
o
Cl-1
Ionic Bonds
the attractive force between oppositely charged ions, which form when electrons are transferred
electrons are transferred from cations to anions
-
-
sodium chloride (NaCl), common table salt
occurs between a metal and a nonmetal
Covalent Bond
a bond formed when atoms share one or more pairs of electrons
positive nucleus is attracted to shared negative electrons
covalent compound – compound form the sharing of electrons
Polar Covalent Bonds
a covalent bond that is formed by the unequal sharing of electrons
one atom will have a stronger attraction for electrons than another atom
water (H2O)
o
oxygen attracts electrons stronger than hydrogen
o
oxygen end is more negative
o
hydrogen end is more positive
Mixtures
a combination of two or more substances not chemically combined
substances in a mixture keep their individual properties
can be separated by physical means
Heterogeneous Mixture
substances are not uniformly distributed
granite is an example
Homogeneous Mixture
mixtures where individual components are uniformly distributed
known as solutions
any sample of a solution will be the same as any other sample (i.e. sea water)
gases and solids can be solutions
alloy – a solution composed of two or more solids
o
brass
o
10K gold
o
steel