Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$\text{Average atomic mass} = (\text{mass}_1 \times \text{fraction}_1) + (\text{mass}_2 \times \text{fraction}_2)$

Question 1

Which scientist is credited with proposing that the atom is mostly empty space with a dense, positively charged nucleus at its center?

Accepted Answer

Ernest Rutherford

Question 2

Which of the following statements best describes the difference between metals and nonmetals?

Accepted Answer

Metals are good conductors and malleable; nonmetals are brittle and poor conductors.

Question 3

Which of the following is the correct definition of atomic number?

Accepted Answer

The number of protons in the nucleus of an atom.

Question 4

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it have?

Accepted Answer

18

Question 5

Which element is a noble gas?

Accepted Answer

Neon

Question 6

Which scientist used a gold foil experiment to discover the nucleus?

Accepted Answer

Ernest Rutherford

Question 7

What is the charge of a sodium ion ($\mathrm{Na^+}$) formed from a neutral sodium atom?

Accepted Answer

$+1$

Question 8

Which of the following elements is an alkaline earth metal?

Accepted Answer

Magnesium

Question 9

An isotope of carbon has a mass number of 14 and an atomic number of 6. What is the number of neutrons in this isotope?

Accepted Answer

8

Question 10

Which of the following best describes the contribution of J. J. Thomson to atomic theory?

Accepted Answer

He discovered the electron using the cathode ray tube.

Question 11

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$	ext{Average atomic mass} = (	ext{mass}_1 	imes 	ext{fraction}_1) + (	ext{mass}_2 	imes 	ext{fraction}_2)$

Question 12

Which of the following elements is a transition metal?

Accepted Answer

Copper

Question 13

Which property is NOT characteristic of metals?

Accepted Answer

Brittle if solid

Question 14

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

Question 15

If an atom has 15 protons, 16 neutrons, and 15 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number: 15, Mass number: 31

Question 16

Which of the following elements is a halogen?

Accepted Answer

Fluorine

Question 17

Which scientist performed the oil drop experiment to determine the charge of an electron?

Accepted Answer

Robert Millikan

Question 18

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 19

A sample contains two isotopes of magnesium: $^{24}\mathrm{Mg}$ (78.99%) and $^{26}\mathrm{Mg}$ (21.01%). What is the average atomic mass of magnesium? (Round to two decimal places)

Accepted Answer

$24.42$

Question 20

Which of the following best describes the periodic table group that contains elements with similar chemical properties and the same number of valence electrons?

Accepted Answer

Group

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