Pre - Chemistry week 3
protons
# of electrons = # of
Condensing
(gas to liquid)
Depositing
(gas to solid)
Vaporization or boiling
(liquid to gas)
Freezing
(liquid to solid)
Subliming
(solid to gas)
Melting
(solid to liquid)
In the lab
, formation of a precipitate, a color change, gas bubbles, or a release of heat are evidence of chemical change. Note that physical changes can give the same evidence as chemical change (for example, boiling makes gas bubbles), so it takes practice and experience to recognize the difference.
Pure substances
- made up of one substance that cannot be physically separated.
compounds
2 or more different atoms bonded together
Heterogeneous Homogeneous
2 types of mixtures
Compounds elements
2 types of pure substances are:
solid liquid gas
3 states of matter
physical property
A _________property does not change the chemical composition of a substance.Examples include color, odor, boiling point, density, conductivity, and physical state.
number and type of atoms in a molecule
A chemical formula tells the
they tend to become positively charged in compounds.
A chemical property of metals
they tend to become negatively charged in compounds.
A chemical property of nonmetals is
nonmetal atoms
A molecule is made up of two or more
isotopes
Atoms of the same element that have different numbers of neutrons
CHANGES IN PHYSICAL STATE OF MATTER
CHANGES IN PHYSICAL STATE OF MATTER
Periodic Table of the Elements
Chemists organize matter on
condensing, then freezing (or depositing
Decreasing the temperature of a gas causes
name and symbol
Elements on the periodic table have a name and a symbol. The symbol is from 1 to 3 letters long where the first letter is capitalized and the remaining letters are lowercase.
law of multiple proportions
If two elements combine to form different compounds, the ratio of masses of the second element that react with a fixed mass of the first element will be a simple, whole-number ratio
melting, then vaporization or subliming
Increasing the temperature of a solid causes
gas
Matter is far apart and uniformly distributed in container Indefinite shape that assumes shape of container Compressible Indefinite volume Most energy
Liqued
Matter loosely packed and moves past itself Indefinite shape that assumes shape of container Incompressible Definite volume Intermediate energy
Solid
Matter tightly packed Definite shape In-compressible Definite volume Least energy
parts of periodic table
Metals appear to the left of the metalloids and include aluminum (Al) Nonmetals appear to the right of the metalloids
Facts about elements:
Of the more than 100 elements, 81 are stable. About 10 elements account for 95% of the mass of the Earth's crust Oxygen accounts for about 50% of the mass of the Earth's crust and about 65% of the mass of the human body
formulas
Some chemical formulas use parenthesis to indicate more than one of a particular unit. For instance, the formula for antifreeze is C2H4(OH)2, which consists of 2 OH units. The atom count is 2 carbon atoms, 6 hydrogen atoms, and 2 oxygen atoms (a total of 10 atoms).
increasing temperature
Substances change state with
compounds always contain the same proportions of elements by mass. For example, sodium chloride is always 39.3% sodium and 60.7% chlorine by mass
The Law of Definite Composition states
chemical formula
The chemical formula can be written from a description of the composition. example, the molecule niacin consists of 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom. The chemical formula is C6H6N2O. As before, subscripts indicate the number of atoms in the formula (when only one atom of a given type is present, no '1' is written).
atomic number
The periodic table is arranged by
atomic mass
The total mass of the protons, neutrons, and electrons in a single atom when it is at rest.
mixtures pure substances
Two classifications of matter
Homogeneous
Type of mixture - the same throughout, like salt dissolved in water (paint, solutions)
Ants Have No Fear Of Ice Cold Beer
acronym for diatomic elements Hydrogen (H2 Nitrogen (N2 Fluorine (F2) Oxygen (O2) Iodine (I2) Chlorine (Cl2) Bromine (Br2)
Metalloids
appear with an edge of their box on the stepped line of the periodic table and include B, Si, Ge, As, Sb, Te, Po, and At. Note that Al also appears on the stepped line but Al is an exception. Al is a metal.
Compounds
can be chemically separated into elements
mixtures
can be physically separated into pure substances
Elements All known elements appear on the Periodic Table of the Elements
can not be broken down by chemical reactions.
Chemical properties
describe the chemical reactions that a substance could undergo (or not undergo), meaning that the composition of elements changes.
compounds always contain the same proportions of elements by mass
gaseous elements have symbols with an italic font, liquid elements have symbols with an outline font, and solids have symbols with a Times-Roman font.
Matter
has mass and occupies space
Metalloids
have physical and chemical properties in between metals and nonmetals.
covalent bond
is a chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as
Chemical Change
means that a chemical reaction occurred. -A chemical property means that the reaction could occur, -whereas a __________ means it did occur.
Physical Change
means to change the physical state or shape of a substance without changing its chemical composition
diatomic elements
molecules composed of only two atoms, of either the same or different chemical elements -covalent
electrons
negative almost to small to measure occupy enormous volume
neutrons
nuetral add with protons for total mass
high density, high luster, high melting point, good conductors of heat and electricity, malleable (can be hammered into sheets), and ductile (can be drawn into wires).
physical properties of metals include
low density, dull, low melting point, poor conductors of heat and electricity, not malleable, not ductile, and 11 nonmetals occur in the gaseous state.
physical properties of nonmetals include
protons
positive identified by atomic number
elements
represented by chemical symbols mostly solids at room temperature mostly metallic arranged by increasing atomic number
law of definite composition
samples of a pure compound always contain the same elements in the same mass proportion.
atom
smallest representation of an element
Heterogeneous
type of mixtures - different throughout, like sand and water (salad)