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Main Idea: What are atoms made of? How do atoms differ?
Atoms - The smallest unit of an element that can still be identified as that element
 Nucleus - center of the atom, contains protons and neutrons
 Proton – has positive electrical charge
 Neutron – has no electrical charge
 Electron – has negative electrical charge, orbits the nucleus
 Atomic number – equal to the number of protons in an atom, determines the type of element
 Protons, neutrons, and electrons are referred to as subatomic particles
Models of the Atom
 Throughout history scientists have built their ideas on the ideas of other scientists.
Isotopes
 Have the same number of protons but different numbers of neutrons.
 Atomic mass = protons + neutrons
Main Idea: What is an element? How are elements classified?
Elements - A substance that contains only one kind of atom
 Characteristics of an element:
o All atoms have the same atomic number which is the same as the number of protons.
o Can’t be broken down into simpler substances
 The most abundant elements are those with low atomic numbers.
 Scientists hypothesize that all other substances were formed from hydrogen.
 Subatomic particles combine in a process called fusion.
 Elements are classified according to their characteristics.
o Metals = conduct electricity, are malleable, and are often shiny
o Nonmetals – do not conduct electricity and are not malleable
The Periodic Table
 Distinguishing elements: metals or nonmetals, solid, liquid, or gas, color, odor
 Organized into the periodic table and arranged by atomic number.
o Different colors identify solids, liquids, gases and synthetic (man-made) elements
 Periodic Table Entry show atomic number, symbol, name, and atomic mass
o Family = each column, have similar properties
o Period = each row, have similar arrangement of electrons
McGuire 2010-2011
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Main Idea: How are compounds formed?
Compounds - A substance made of atoms of two or more elements that are chemically combined.
 The chemical formula for a compound shows the elements that are in it.
SiO2 = 1 atom of silicon + 2 atoms of oxygen = sand
NaCl = 1 atom of sodium + 1 atom of chlorine = table salt
 Compounds don’t have the same properties as the elements that form them.
H20 = 2 atoms of hydrogen + 1 atom of oxygen = water (gas + gas = liquid)
 Compounds hold together because atoms bond (attach) to one another.
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Share electrons. (Example: water)
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Electrons have moved from the atoms of one element to the atoms of another.
Positive charged atoms are attracted to negative charged atoms. (Example: table salt)
Compounds in Nature and Industry
 Air = 78% nitrogen and 21% oxygen
 Ores = metals + silicon + oxygen so must be treated to remove the metals
 Organic Compounds = carbon combined with other elements, form living things
Main Idea: How do solids, liquids and gases differ?
States of Matter
 Solid = definite volume, definite shape, molecules do not move around much because they are
arranged in a fixed pattern
o examples: ice, snow
 Liquid = definite volume, shape is not definite, takes the shape of the container that holds it, more
energy than the solid state, can flow (fluid)
o examples: rain, mist, clouds, steam
 Gas = volume is not definite, shape is not definite, expands to fill the container that holds it,
o example: water molecules in the air cannot be seen
Molecules - Bonded (joined) atoms are called molecules
 Solids, liquids and gases look and act differently because of the energy, or motion of their atoms or
molecules
Changes of State - The atoms of ALL elements and compounds can exist as solids, liquids, and gases.
 The melting point is the point at which a solid changes to a gas
o ice becomes water at 0  C which is 32  F
 The boiling point is the point at which a liquid changes to a gas
o water becomes water vapor at 100  C which is 212  F
 Increasing temperature changes a solid to a liquid (melting), or a liquid to a gas (evaporation)
 Decreasing pressure changes a solid to a liquid (melting), or a liquid to a gas (evaporation)
 Sublimation = a solid changes directly to a gas with no melting
Plasma = the most common form of matter in the universe
 When gases become very hot the atoms gain energy and lose electrons
o Atoms have a positive charge and “free” electrons.
 Examples of plasma: stars, auroras, the inner core of a flame, lightning, fluorescent bulb
 On the sun, fusion is the nuclei of atoms uniting = releases a great amount of energy
McGuire 2010-2011