Unit 3 Atomic Structure and Radioactivity(Chem)

Found in the nucleus

• Protons

• Neutrons

• protons and neutrons

• electrons and protons

a nitrogen atom that has gained three electrons

• Mg

• Phosphorus-28

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If 75% of the isotopes of an element have a mass of 35.0 amu, and 25% have a mass of 37.0 amu, what is the average atomic weight?

• 35.0 amu

• 35.5 amu

• 36.0 amu

• 37.0 amu

All neutral atoms in a given sample of an element contain the same number of

• protons and electrons

• proton and neutrons

• neutrons

• electrons

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Hydrogen has three isotopes with mass numbers of 1, 2, and 3, and has an average atomic weight of 1.00794 amu. From this you can conclude that

• Most H atoms have a mass number of 1

• More H atoms have a mass number of 2 than 1 or 3

• The three isotopes occur in equal abundances

• isotopes only have a mass of 1

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Why are most atomic masses on the periodic table decimal numbers?

• Only parts of a neutron are present in some atoms

• Electrons only have a mass of 0.25 amu

• They are a weighted average of naturally occurring isotopes

• They are estimates

The average atomic weight of Neon is

• 22.99

• 21

• 90.0

• 20.18

Element X has two naturally occurring isotopes: X-24 (15%) and X-26 (85%). Why is 25 not a reasonable estimate for the average atomic weight?

• X-26 is much more abundant

• X-24 is much more abundant

• The average must be higher than the heaviest isotope

• 25 is a reasonable estimate

Which statement correctly describes the charge of the nucleus and electron cloud?

• Nucleus is positive, electron cloud is negative

• Nucleus is neutral, electron cloud is negative

• Nucleus is negative, electron cloud is negative

• Nucleus is positive, electron cloud is neutral

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An atom is electrically neutral when

• there are no protons

• there are no electrons

• the number of protons and electrons is equal

• there are more neutrons than protons