Chemistry Chapter 2

What is the first letter in a chemical symbol for an element?

Always capitalized; the second letter, if any, is lowercase.

What does a chemical formula represent?

The relative number of each type of element in a compound.

What does the Law of Conservation of Mass state?

Matter is neither created nor destroyed during chemical reactions.

Who conducted a quantitative experiment demonstrating the Law of Conservation of Mass?

Antoine Lavoisier.

What does the Law of Definite Proportions state?

Any given compound is composed of definite proportions by mass of its elements.

How is the percent by mass of an element in a compound calculated?

It is the ratio of the mass of the element to the total mass of the compound, multiplied by 100%.

What is an example of the Law of Definite Proportions using water?

Water (H₂O) always contains hydrogen and oxygen in a fixed mass ratio of 2:16.

What does the Law of Multiple Proportions state?

For compounds composed of the same elements, the ratio of the masses of any other element is a small, whole-number ratio.

In the comparison of CO and CO₂, how does the mass of oxygen relate to carbon?

CO₂ contains twice as much oxygen as CO for a fixed mass of carbon.

What is Dalton's Atomic Theory?

Each element is made of atoms, which are identical for a given element and different for different elements.

What modern revisions have been made to Dalton's Atomic Theory?

Atoms are divisible, and isotopes show that not all atoms of the same element have the same mass.

What was demonstrated in J.J. Thomson's Cathode Ray Tube Experiment?

Rays emitted from the cathode are negatively charged particles called electrons.

What did J.J. Thomson determine about electrons?

He proposed they are negatively charged particles and calculated their charge-to-mass ratio.

How did R. A. Millikan determine the charge on an electron?

By examining the motion of tiny oil drops.

What is the charge-to-mass ratio of an electron?

-1.76 × 10^8 C/g.

What is the significance of the chemical symbols in the periodic table?

They represent elements and their combinations in compounds.

What is the role of chemical reactions according to Dalton's theory?

They involve the reorganization of atoms without changing the atoms themselves.

What is the mass ratio of hydrogen to oxygen in water?

1:8.

What happens to the mass of elements during a chemical reaction?

The total mass remains constant.

What is the relationship between the mass of carbon and the mass of oxygen in CO and CO₂?

For the same mass of carbon, the masses of oxygen in CO₂ and CO are in a small whole-number ratio of 2:1.

What is a compound?

A substance formed when atoms of different elements combine.

What does the term 'isotope' refer to?

Atoms of the same element that have different masses due to varying numbers of neutrons.

What is the significance of the phosphor-coated surface in Thomson's experiment?

It reveals the path of the cathode ray by producing bright light when struck.

What does the term 'chemical formula' indicate?

The types and numbers of atoms in a molecule.

What is the percent composition of nitrogen in nitrogen monoxide (NO)?

46.68% nitrogen by mass.

What is the fixed mass ratio of hydrogen to oxygen in water?

2.00 g of hydrogen combines with 16.00 g of oxygen.

What is the main conclusion of the Law of Multiple Proportions?

The mass ratios of elements in different compounds can be expressed as small whole numbers.

What is the charge-to-mass ratio of cathode rays?

−1.76 × 10^8 C/g

What is the charge of an electron?

-1.6022 × 10^-19 C

What are cathode rays now known to be?

Beams of electrons

What is the mass of an electron?

9.11 × 10^-31 kg

What did Dalton's model of the atom consist of?

An indivisible sphere

What is Thomson's plum-pudding model?

A model consisting of negatively charged electrons suspended in a larger sphere of positive charge

Who discovered radioactivity?

Henry Becquerel

What types of particles did Marie Curie identify in her studies of radioactivity?

Alpha (α), beta (β), and gamma (γ) particles

What did Rutherford predict about alpha particles?

They would pass through atoms without being stopped

Where is the positive charge and majority of mass located in Rutherford's model?

In a small area called the nucleus

What is the relationship between protons and electrons in an electrically neutral atom?

The number of protons equals the number of electrons

What is the atomic number (Z)?

The number of protons in an atom's nucleus

What is the mass number (A)?

The sum of protons and neutrons in the nucleus (A = p + n)

What are isotopes?

Atoms with the same number of protons but different numbers of neutrons

How do isotopes of the same element behave chemically?

They exhibit identical chemical properties; only the mass differs

What is the formula to calculate the number of neutrons?

n = A - Z

What is the charge of a proton?

+1

What is the charge of a neutron?

0 (neutral)

What is the mass of a proton in atomic mass units (u)?

1.0073 u

What is the mass of a neutron in atomic mass units (u)?

1.0087 u

What is the mass of an electron in atomic mass units (u)?

0.000549 u

What is the significance of the periodic table?

It groups elements with similar chemical characteristics and arranges them by increasing atomic number

What does each square on the periodic table represent?

One element

What is the relationship between mass number and atomic number?

Mass number (A) is the sum of protons (Z) and neutrons (n)

What is the atomic nucleus?

The small, dense center of an atom containing protons and neutrons

What is the volume occupied by electrons in an atom?

Almost all the volume of the atom

What defines the atomic number of an element?

The number of protons in the nucleus.

What is the chemical symbol for lead?

Pb

What does the average atomic mass represent?

The weighted average of naturally occurring isotopes of an element.

What is the charge of noble gases?

Charge = 0; they do not react.

What charge do halogens typically have?

Charge = -1

What charge do alkali metals typically have?

Charge = +1

What charge do alkaline earth metals typically have?

Charge = +2

What are cations?

Atoms with positive charges.

What are anions?

Atoms with negative charges.

What is the atomic mass scale based on?

It is relative, with one isotope assigned a value (C-12 = 12 u).

How is the atomic mass of an element calculated?

It is the weighted average of the masses of its naturally occurring isotopes.

What is the natural fractional abundance of ¹²C?

0.9893 (98.93%)

What is the atomic number and mass number of calcium?

Atomic Number = 20; Mass Number = 40

What is the atomic mass of calcium?

40.08 u

How many protons and electrons are in F−?

9 protons and 10 electrons.

How many protons and electrons are in Mg²⁺?

12 protons and 10 electrons.

How many protons and electrons are in N³⁻?

7 protons and 10 electrons.

How many protons and electrons are in W⁶⁺?

74 protons and 68 electrons.

What is the relationship between mass numbers and atomic masses?

Mass numbers are whole numbers, while atomic masses on the periodic table are decimals.

What is the formula for calculating the weighted average atomic mass?

Weighted average = Σ(fraction of isotope × isotope mass).

What is an example of a compound with two atoms of oxygen for every atom of carbon?

CO₂ (carbon dioxide).

What is the relative number of atoms in PCl₃?

Three atoms of chlorine for every atom of phosphorus.

What happens to sodium atoms in ionic bonding?

They lose an electron to form a positively charged sodium cation.

What happens to oxygen atoms in ionic bonding?

They gain electrons to form a negatively charged oxide anion.

What is the charge of an atom that has lost an electron?

It becomes a cation (positively charged).

What is the charge of an atom that has gained an electron?

It becomes an anion (negatively charged).