Mrs. P Science 8 Exam TKA (Regular)


Terms in this set (...)

*Proposed the idea that matter is formed of small pieces that could not be cut into smaller pieces.
*Around 430 B.C.
*A Greek philosopher
Dalton's Theory
Inferred that atoms had certain characteristics
J.J. Thompson
1897: found that atoms contained negatively charged particles. He proposed the muffin model (negative charges scattered throughout a ball of positive charge)
1911: student of Thompson
*He aimed positively charged particles at a sheet of gold foil
*Like charges repel
*He inferred that an atom's positive charge must be clustered in the center. (The positively charged particles are protons)
Bohr's Model
1913: He showed that electrons could have only certain amounts of energy leading them to move in certain orbits
Ex. Onion layers
Atomic number
The number of protons in the nucleus of an atom
Atoms with the same number of protons but different number of neutrons
Mass number
The sum of the protons and the neutrons in the nucleus
Mendeleev's Work
Noticed a pattern of properties appeared when he arranged the elements in order of increasing atomic mass
The modern periodic table
We arrange our modern table in order of atomic number increasing - NOT atomic mass
From left to right the properties of the elements change in a pattern
18 vertical columns
Reading an element's square
Chemical symbol, atomic mass, atomic number, and name are all included in the element's square
How elements from in stars
Nuclear fusion combine smaller nuclei into larger nuclei into larger nuclei creating heavier elements
Physical and chemical properties of metals
They are to the left of the zigzag line
*most are shiny
*Most with magnetism
*Most are solid at room temp
*Usually react by losing electrons to other atoms Ex. sodium is very reactive and gold and platinum are very not reactive
The Alkaline Metals
Group 1: react w/ other elements by losing 1 electron
*never found uncombined in nature bc they are so reactive
*soft and shiny
*2 most important are sodium and potassium
Alkaline earth metals
Group 2: fairly hard, grey/white, good conductors, reacts by losing 2 electrons, never found uncombined, 2 most common: magnesium and calcium
Transition metals
Groups 3-12: Ex. Iron, copper, nickel, and gold
*hard and shiny
*good conductors
Metals in mixed groups
Group 13-15: most common: aluminum, tin, and lead
Top row of the bottom 2 rows, named after the first element in the row, soft, malleable, shiny metals with high conductivity
Below lanthanides, only the first 4 occur naturally on earth, the rest are synthetic
a mixture of metals
Physical and chemical properties of nonmetals
*poor conductors
* dull and brittle
*to the right of the zigzag line
*there are 17 nonmetals
*10 are gases at room temperature
*Bromine is the only liquid nonmetal
*Most nonmetals are reactive and the most reactive is Flourine
*Group 18 rarely reacts at all
*Atoms of nonmetals usually gain/share electrons when they react with other atoms
*When metals and nonmetals react electrons move from the metal to the nonmetal atoms
Carbon family
Group 14: 4 valance electrons in outer shell
*most of the fuels that are burned fro energy contain carbon
Nitrogen family
Group 15: 5 valance electrons
*family needs 3 more to become stable
*atmosphere is almost 80% nitrogen
*Diatomic molecule consists of 2 atoms
*Nitrogen Fixation: certain bacteria can use nitrogen to form compounds that plants can take up from the soil and use it
Oxygen family
Group 16: 6 valence electrons
need 2 more to be stable triatomic consists of 3 atoms in the upper atmosphere and screens out harmful radiations from the sum
*Oxygen is most abundant in the earth's crust and 2nd most abundant in the atmosphere
*sulfur is mainly used to make rubber tires
Halogen family
Group 17: & valance electrons
* Most reactive nonmetals
*As compound s they are very useful Ex. nonstick cooking spray
Nobel gases
Group 18: don't react
*8 valance electrons
*weren't discovered until late 1800s
alone in the upper left corner
*1 proton and 1 electron
*extremely reactive
*usually found combined w/ oxygen in water
*on zigzag line
*some characteristics of both nonmetals and metals
*most common is silicon
*sand which is silicon dioxide is the main component of glass
*most useful property of metalloids ids their varying ability top conduct electricity
Semi conductor
substances that conduct electricity under certain conditions but not under other conditions
Valance electrons
the electrons that are int the highest energy level of an atom that are involved in chemical reactions
Electron dot diagram
a representation of the valance in an atom using dots
How the periodic table table works
The periodic table gives you information about the arrangement of electrons in atom
Ionic bond
the attraction between two oppositely charged ions
Covalent bonds
The chemical bonds formed when 2 atoms share electrons
How ions form
When electrically charged particles lose or gain electrons
Polyatomic ions
*Ions that are made of more than 1 atom
*Group of atoms that act as 1 unit
*the entire unit has a charge on it
Chemical formulas
a combination of symbols that show the ratio of elements in a compound
Naming ionic compounds
The name of the positive ion (metal) comes first followed by the negative ion (nonmetal)
Properties of ionic compounds
*ions form in an orderly 3D arrangement called a crystal
*every ion is attracted to ions of opposite charge this makes the bonds very strong
*high melting points and boiling points
*solid at room temp
*when ionic crystals dissolve in water the bonds between the ions are broken
Properties of molecular compounds
*low melting and boiling points
*most are liquids or solids at room temp
*poor conductivity
Covalent bonds: Polar and nonpolar?
Polar: electrons are shared unequally(bully)
Nonpolar: electrons are shared equally (same number of valance electrons)
Metallic bonding
When metals lose their valance electrons they become positively charged ions. Each metal ions held in the crystal by a metallic bond
*Metallic bond: attraction between a positive metal ion and the electrons surrounding it
all types of steel are made with?
anything that has mass and takes up space
Properties of matter
Changes of matter can be described as chemical or physical.
Physical change
any change that alters appearance of a substance but does not change the substance into something else
Chemical change
change in matter that produces one or more new substances is a chemical change, or chemical reaction.
5 evidences that a chemical reaction may have occurred
*Color change
Endothermic reaction
reaction in which energy is absorbed (chemical cold pack)
Exothermic reaction
a reaction that releases energy in heat
the substances you have at the beginning of an experiment
When the reaction is complete you have new substances called products
Chemical equation
use formulas to represent the substances involved in a reaction
Conservation of mass
states that during a chemical reaction, matter is not created or destroyed.
Open system vs. closed system
open: matter can enter from or escape the surroundings
closed: matter is not allowed to enter or leave
Balancing chemical equations
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.
a number placed in front of a chemical formula in an equation
What are the 3 classifications of chemical reactions?
Synthesis, decomposition, and replacement
5 factors that affect the rate of chemical reactions
Surface energy, temperature, consentration, catalysts, and inhibitors
Fire triangle
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Fire safety: the best way to practice fire safety is...
Fire prevention
well mixed mixture that contains a solvent and at least one solute
part of the solution present in the largest amount (does the dissolving)
substance present in the smaller amount and gets dissolved
in the middle of a solution, mixture containing small, undissolved particles that do not settle out (the particles are large enough to scatter a light beam)
mixture in which particles can be seen and easily separated by settling or filtration
solutes ______ the freezing point of a solvent
solutes_______ the boiling point of a solvent
dilute vs concentrated solution
diluted: a mixture that has only a little solute dissolved in a certain amount of solvent
concentrated: one that has a lot of solute dissolved in the solvent
the measure of how much solute can dissolve in a solvent at a given time
saturated vs unsaturated
saturated: when you've added so much solute that no more can dissolve
unsaturated: if you're still able to dissolve more solute than it is unsaturated
pressure/temperature affecting solubility
pressure: the higher the pressure of the gas over the solvent the more gas that can dissolve
temperature: for most solids, solubility increases as the in temperature increases. unlike most solids, gases become soluble when the temperature gets colder
acids/ bases
acids: an acid is a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus paper red. Carbon dioxide gas is produced when an acid reacts with a carbonate. produces hydrogen ions in water.
base: a substance that tastes bitter, feels slippery and turns red litmus paper blue. a base is any substance that produces hydroxide ions in water.
compound that changes color when in contact with an acid or base
when an acid and base mix: what is made
water and a type of salt
what is digestion
there are 2 types:
mechanical-teeth tearing food
chemical-takes place with help of enzymes. Enzymes need the right temp and pH to do their job
On the pH scale, what number is most acidic, basic, and what is nuetral
zero is most acidic, 14 is most basic, 7 is neutral