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Matter that has
the same composition and properties throughout is called a
substance.

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A proton is a positively
charged particle present in the nucleus of all atoms. The rest of
each atom is empty space occupied by the atom’s almost mass less
electrons.

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Nonmetals are elements that are usually dull in appearance. Most are poor conductors of heat and electricity. Many are gases at room temperature, and bromine is a liquid.

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It was proposed that another particle must be in the nucleus
to account for the extra mass. The particle, which was later
called the neutron (NEW trahn), would have the same mass as
a proton and be electrically neutral.

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When two or more substances (elements or compounds) come together but don’t combine to make a new substance, a mixture results.

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Metalloids are elements that have characteristics of metals and nonmetals. On the periodic table, metalloids are found between the metals and nonmetals

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Metals generally have a shiny or metallic luster and are good
conductors of heat and electricity. All metals, except mercury, are
solids at room temperature. Metals are malleable (MAL yuh bul),
which means they can be bent and pounded into various shapes.

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An atom’s mass number is the number
of protons plus the number of neutrons it contains. The numbers
35 and 37, which were used to refer to chlorine, are mass numbers.
Hydrogen has three isotopes with mass numbers of 1, 2, and 3.

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These two
types of chlorine atoms are chlorine-35 and chlorine-37. They
are called isotopes (I suh tohps), which are atoms of the same
element that have different numbers of neutrons

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An element is matter made of atoms of only one kind.

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Electrons travel in a region surrounding the nucleus,
which is called the electron cloud.

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Negatively charged particles are called electrons.

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A compound is a
substance whose smallest unit is made up of atoms of more than
one element bonded together.

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The top number is the element’s
atomic number. It tells you the number of protons in the nucleus of each atom of that element.

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The atomic mass is the weighted average mass of the isotopes of an element