Unit 2 Chemistry

An atom is

• the smallest unit of matter that maintains its chemical identity.

• the smallest unit of a compound.

• always made of carbon.

• smaller than an electron.

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Which of the following statements is true according to modern atomic theory?

• Atoms of the same element may have different masses.

• Atoms may be divided in ordinary chemical reactions.

• Atoms can never combine with any other atoms.

• Cathode rays are composed of protons..

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A positively charged particle with mass 1.673 ´ 10–24 g is a(n)

• proton.

• neutron.

• electron.

• positron.

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A nuclear particle that has about the same mass as a proton, but with no electrical charge, is called a(n)

• nuclide.

• neutron.

• electron.

• isotope.

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The nucleus of an atom has all of the following characteristics except that it

• is positively charged.

• is very dense.

• contains nearly all of the atom's mass.

• contains nearly all of the atom's volume.

An atom is electrically neutral because

• neutrons balance the protons and electrons.

• nuclear forces stabilize the charges.

• the numbers of protons and electrons are equal.

• the numbers of protons and neutrons are equal.

Most of the volume of an atom is occupied by the

• nucleus.

• nuclides.

• electrons.

• protons.

The charge due to the electrons of a neutral atom

• prevents compounds from forming.

• balances the charge on the nucleus.

• attracts electrons in other atoms.

• does not exist.

The smallest unit of an element that can exist either alone or in combination with other such particles of the same or different elements is the

• electron.

• proton.

• neutron.

• atom.

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Isotopes are atoms of the same element that have different

• principal chemical properties.

• masses.

• numbers of protons.

• numbers of electrons.