Question 1

Which experiment led to the discovery of the electron, and what was the key observation that supported this discovery?

Accepted Answer

Thomson's cathode ray tube experiment; the beam was deflected toward the positive plate, indicating negatively charged particles.

Question 2

According to Dalton’s atomic theory, which statement is correct?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 3

Which subatomic particle defines the identity of an element?

Accepted Answer

Proton

Question 4

A neutral atom of sodium (Na) has 11 protons. How many electrons does it have?

Accepted Answer

11

Question 5

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation has more protons than electrons; an anion has more electrons than protons.

Question 6

Which element is classified as a metalloid?

Accepted Answer

Silicon (Si)

Question 7

What is the charge of a magnesium ion with 10 electrons?

Accepted Answer

$$+2$$

Question 8

Which of the following pairs are isotopes?

Accepted Answer

$$^{238}_{92}\mathrm{U}$$ and $$^{235}_{92}\mathrm{U}$$

Question 9

Calculate the atomic mass of silver if it has two naturally occurring isotopes: Ag-107 ($$106.90509$$ amu, $$51.84\%) $$and Ag-109 ($$108.90476$$ amu, $$48.16\%).$$

Accepted Answer

$$107.87$$ amu

Question 10

Which group in the periodic table contains the most reactive nonmetals?

Accepted Answer

Group VIIA (Halogens)

Question 11

What is the mass number ($$A) of a $$chromium isotope with 24 protons and 28 neutrons?

Accepted Answer

$$A = 52$$

Question 12

Which element has the chemical symbol 'K' and what is its classification?

Accepted Answer

Potassium, metal

Question 13

A neutral atom of phosphorus (P) has 15 protons and 15 electrons. What is the electron count for a $$\mathrm{P}^{3-}$$ ion?

Accepted Answer

18

Question 14

Which statement about the periodic table is correct?

Accepted Answer

Elements with similar properties are grouped in columns.

Question 15

What is the atomic number ($$Z$$), mass number ($$A$$), and symbol for the carbon isotope with 7 neutrons?

Accepted Answer

$$Z = 6$$, $$A = 13$$, $$^{13}\mathrm{C}$$

Question 16

Which of the following is a property of metals?

Accepted Answer

Malleable and good conductors of heat

Question 17

If an atom has 20 protons, 22 neutrons, and 18 electrons, what is its charge?

Accepted Answer

$$+2$$

Question 18

Which element is a noble gas and what is its typical chemical reactivity?

Accepted Answer

Argon; very unreactive

Question 19

What is the average atomic mass of copper if it is 69.17% Cu-63 ($$62.9396$$ amu) and 30.83% Cu-65 ($$64.9278$$ amu)?

Accepted Answer

$$63.55$$ amu

Atoms and Elements: Structure, Classification, and Isotopes

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