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Unit 2 Study Guide

Democritus believed that the universe was made of empty space and tiny bits of stuff. He called these tiny bits of stuff “atoms.”
Antoine Lavoisier came up with the law of conservation of matter
volume measured in cubic meters
matter measured in grams
Density mass/volume
model a representation of an object, event, or idea
Physical models can be seen or touched (Ex.: a globe)
Computer models can be seen on a computer screen (Ex.: moving weather patterns on a computer)
Idea Models concepts that describe how someone thinks about something in the natural world (Ex: Einstein’s E=mc2)
John Dalton All elements are composed of atoms. Atoms are indivisible and indestructible particles
John Dalton Atoms of the same element are exactly alike
John Dalton Atoms of different elements are different
John Dalton Compounds are formed by the joining of atoms of two or more elements
J.J. Thomson discovered negatively charged electrons using a cathode ray tube.
J.J. Thomson placed a magnet around the tube causing the light beam to bend
Ernest Rutherford conducted his gold foil experiment.
Ernest Rutherford discovered the positively-charged center of the atom
Ernest Rutherford determined that atoms were mostly empty space.
James Chadwick One of Ernest Rutherford's students
James Chadwick discovered neutrons in the nucleus of the atom
Niels Bohr proposed that electrons were located in specific energy levels and that electrons traveled in definite orbits around the nucleus.
Electron Cloud Model current model of the atom
Electron Cloud Model The darker the cloud (closer to the nucleus), the higher the probability that the electrons will be there
Dmitri Mendeleev made the first periodic table
Dmitri Mendeleev arranged the table by the atomic mass
How is today's periodic table arranged? by the atomic number
horizontal rows periods
How do you figure out what horizontal row an element is on? by the amount of dots on the outer period
vertical columns groups, or families
How do you figure out what column an element is on? the amount of electrons
How many rows are there? 7
How many column are there? 18
Metalloids “stair step” line between the metals and nonmetals
Metalloids solids at room temperature
Nonmetals brittle
Brittle cannot change shape without breaking
Malleable can be bent and pounded into various shapes, or flattened into thin sheets (foil)
Ductile can be drawn into wire without breaking
Proton positively charged particle located in the nucleus of the atom
Neutron neutral charge located in the nucleus of the atom
Electron negatively charged particle located outside the nucleus of the atom
Nucleus the dense central portion of the atom
Proton Its relative atomic mass is 1 atomic mass unit (amu).
Neutron Its relative atomic mass is 1 amu
Electron Its relative atomic mass is 1/1836 amu.
Atomic Number the number of protons in the nucleus of an atom
Isotopes elements with the same number of protons but different numbers of neutrons
The number of electrons are the same number as the? atomic number
Mass Number the sum of the protons and neutrons in the nucleus of an atom. This number is not listed on the periodic table
Average Atomic Mass weighted average mass of all isotopes of an element
Solid any substance with definite shape and volume.
Liquid any substance with definite volume but no definite shape.
Gas any substance with no definite shape or volume
Melting going from a solid to a liquid. Must have an increase in energy. They absorb energy. This is an endothermic process.
Boiling going from a liquid to a gas below the liquid’s surface. Must have an increase in energy. This is an endothermic process.
Evaporation going from a liquid to a gas at the liquid’s surface. Still must have an increase in energy and is endothermic
Sublimation going from a solid to a gas. Requires an increase in energy and is endothermic
Condensation going from a gas to a liquid. Requires a decrease in energy, energy is released and is exothermic.
Thermal Energy the total amount of kinetic and potential energy of an object.
Heat the movement of thermal energy from hot to cold. Heat always moves from hot to cold
Temperature the average kinetic energy of all the particles in an object.
Physical Property a characteristic of a pure substance that can be observed without changing its identity.
Chemical Property a characteristic of a pure substance that describes its ability to change into another substance – change its identity
Physical Change a change that results in a change in appearance or form but not identity
Chemical Change a change that results in a change in the identity of a substance
Endothermic energy is absorbed, feels colder to touch (“Endo” = “in to”)
Exothermic energy is released, feels hotter to touch. (“Exo” = “out of”)
Law of Conservation of Mass Matter cannot be created or destroyed; but only transferred or transformed.
Created by: S732596