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STAAR Reporting Category 1Matter & Energy

Middle School ScienceScience STAAR Need to Know

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Atomic Theory Atoms are building blocks of elements Atoms in each unique element are the same.

(Ex: Every oxygen element has the same # of protons)

Atoms are different from atoms of other elements (Ex: Hydrogen has a different # of protons than oxygen)

Two or more different atoms bond in simple ratios to form compounds (Ex: Hydrogen & oxygen can chemically combine to form water- H2O )

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Atoms and Elements

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Atomic Particle Charges

Protons Positive +Neutrons Neutral =Electrons Negative -

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Location of Subatomic Particles 10-13 cm

electrons

protons

neutrons

10-8 cm

nucleus

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Location of Atomic Particles

Inside the Nucleus

Protons with a Positive chargeANDNeutrons with a Neutral charge –that means they

do not have a charge

Outside the Nucleus- in electron cloud

Electrons with a Negative charge

Did you know electrons are very, very small and move very, very fast???

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Periodic Squares

The periodic square for an element can tell you lots of information about that atom.

Atomic number = # of protons Atomic number = # of electrons

That means in a neutral (uncharged) atom the # of protons and electrons are always the SAME!!!!

11Na

22.99

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Atomic Mass on the Periodic Table

11Na

22.99

Atomic Numberor Protons

Symbol

Atomic Mass orProtons + neutrons

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Atomic number

Atomic number = # of Protons

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Mass Number

The number of

protons and neutronsin an atom

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Number of Electrons

A balanced atom is neutral The net overall charge is zero Number of protons = Number of

electrons Atomic number = Number of

electrons

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Elements with similar properties are placed in the same group in the periodic table.

The stair-step line separates the elements into metals and nonmetals.

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Metals & Nonmetals

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Element Protons

Neutrons

Electrons

2 elements with similar properties

Chlorine-35 17 18 17 F and Br

Iron-56

Magnesium-24

Lead-208

Nitrogen-14

26 30 26 Ru and Os

12 1212 Ca and Sr

82 82126

7 7 7

Sn and Ge

P and As

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Molecules & Compounds

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MixturesCombination of two or more pure substances. Substances are mixed together but have not reacted to form any new molecules.

Example- Sugar (a compound) dissolves in water (a compound) to form a mixture. The molecules of sugar and water do not change chemically. They just become mixed together.

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Properties of matterPhysical properties – can be observed without changing the substance into a different substance.

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Chemical PropertiesCharacteristics of a substance that are observed when it reacts (changes) to produce one or more different substances.

Example- Water can be changed into hydrogen gas and oxygen gas using an electric current. When water molecules change chemically into hydrogen gas and oxygen gas, we say that a chemical change has occurred. Hydrogen gas and oxygen gas each have a different set of properties.

Substances change into different substances through chemical reactions.

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Chemical ReactionsSubstances change into other substances in chemical reactions. The atoms in the original substance are rearranged. The bonds in the original substance may be broken and new bonds may be formed between different atoms. This produces one or more new substances that may be either pure elements or compounds. The products of a chemical reaction always have difference chemical and physical properties than the original substance(s).

Evidence of a Chemical Reaction a change in odor, a change in color, a solid precipitate is formed, a gas is formed, there is either absorption or release of heat

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Chemical Equations

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