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Glossary of Chapter 1 - Atoms and Elements: The Building Blocks of Chemistry

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Physical property
a property that can be observed without changing the chemical makeup of a substance
Physical change
a change that doesn't affect the chemical makeup of the substance
Chemical reaction
a process in which chemicals interact with each other to form entirely different substances with different properties
Extensive property
a property that depends on sample size;
e.g., volume
Intensive property
properties that are independent of sample size;
e.g., color, electrical conductivity, melting point
Decomposition reaction
when a chemical reaction changes one substance into two or more substances
Elements
substances that cannot be decomposed into simpler materials by chemical reactions
Compound
a substance that is composed of two or more different elements in which the elements are always combined in the same fixed proportions by mass
Pure substance
a substance in which the composition is always the same regardless of its source;
e.g., elements and compounds
Mixtures
substances that can have variable compositions
Homogeneous mixture
a mixture with the same properties throughout the sample;
often called a solution
Heterogeneous mixture
a mixture that consists of two or more regions called phases that differ in properties
Law of conservation of mass
no detectable gain or loss of mass occurs in chemical reactions, mass is conserved
Law of definite proportions
in a given chemical compound, the elements are always combined in the same proportion by mass
Dalton's atomic theory
1) matter consists of tiny particles called atoms
2) atoms are indestructible. In chemical reactions, the atoms rearrange but they do not themselves break apart
3) in any sample of a pure element, all the atoms are identical in mass and other properties
4) the atoms of different elements differ in mass and other properties
5) when compouds are formed, the numerical ratio of atoms remains the same
Law of multiple proportions
whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers
Isotopes
different atoms with different mass numbers but similar atomic numbers
Malleability
the ability to be hammered or rolled into thin sheets
Ductility
the ability to be drawn into wire

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