chem test

Who first proposed the idea of the atom?

Democritus, around 400 BC.

What are the six main points of Dalton’s atomic theory?

1. All matter is made of atoms. 2. Atoms of the same element are identical. 3. Different elements have different masses and properties. 4. Compounds form in whole-number ratios. 5. Atoms cannot be created or destroyed in chemical reactions. 6. Chemical reactions rearrange atoms.

Which two points of Dalton’s atomic theory are now disputed?

Atoms are indivisible, and all atoms of the same element are identical.

Why is Dalton’s theory that atoms are indivisible incorrect?

Atoms contain protons, neutrons, and electrons; nuclear reactions can change nuclei.

Why is Dalton’s theory that all atoms of an element are identical incorrect?

Isotopes have different numbers of neutrons.

How did Thomson discover electrons?

Cathode ray experiments showed that atoms contain negatively charged particles.

What atomic model did Thomson propose?

The plum pudding model, with electrons embedded in a positively charged sphere.

What did Rutherford’s gold foil experiment discover?

Atoms are mostly empty space with a small, dense, positively charged nucleus.

Which subatomic particle identifies an element?

Protons.

What is an isotope?

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

How do you calculate mass number?

Mass number = protons + neutrons.

How do you calculate neutrons?

Neutrons = mass number − atomic number.

How do you calculate the charge of an atom or ion?

Charge = protons − electrons.

How do you find electrons in a neutral atom?

Electrons = atomic number.

How do you find electrons in a positive ion?

Subtract the positive charge from the atomic number.

How do you find electrons in a negative ion?

Add the magnitude of the negative charge to the atomic number.

What is the charge of a neutral atom?

Zero; it has equal numbers of protons and electrons.

What is an AMU?

An atomic mass unit used to measure atomic mass.

Approximately how much mass does a proton have?

1 AMU.

Approximately how much mass does a neutron have?

1 AMU.

Approximately how much mass does an electron have?

Almost 0 AMU.

How do you write isotope notation?

Write the mass number at the upper left and atomic number at the lower left of the element symbol.

What is the isotope symbol for carbon-12?

¹²₆C.

What is the isotope symbol for carbon-13?

¹³₆C.

What is the isotope symbol for carbon-14?

¹⁴₆C.

How do you calculate average atomic mass?

Multiply each isotope’s mass by its decimal abundance and add the results.

How do you convert percent abundance into a decimal?

Divide the percentage by 100.

What is the formula for average atomic mass?

Average atomic mass = (mass₁ × abundance₁) + (mass₂ × abundance₂) + …

What must isotope abundances add up to?

100%, or 1.00 as a decimal.

How do you calculate an unknown isotope’s abundance?

Let one abundance equal x and the other equal 1 − x, then solve using the average mass.

An element has isotopes of 100 amu and 104 amu with an average mass of 101 amu. What are their abundances?

100 amu isotope = 75%; 104 amu isotope = 25%.

Lithium-6 has a mass of 6 amu and 7.59% abundance. Lithium-7 has a mass of 7.016 amu and 92.41% abundance. What is the average mass?

(6 × 0.0759) + (7.016 × 0.9241) ≈ 6.939 amu.

What is the difference between mass number and average atomic mass?

Mass number is protons plus neutrons in one isotope; average atomic mass is the weighted average of naturally occurring isotopes.

What is radioactivity?

The release of particles or energy from an unstable atomic nucleus.

What is radioactive decay?

The process in which an unstable nucleus releases radiation to become more stable.

What are the three main types of radioactive emissions?

Alpha, beta, and gamma.

What is the symbol, mass number, and atomic number of an alpha particle?

⁴₂He; mass number 4; atomic number 2.

What is the symbol, mass number, and atomic number of a beta-minus particle?

⁰₋₁e; mass number 0; atomic number −1.

What is the symbol, mass number, and atomic number of gamma radiation?

⁰₀γ; mass number 0; atomic number 0.

Which radioactive particle has the greatest mass?

Alpha.

Which type of radioactive emission has the greatest penetrating power?

Gamma.

Which type of radioactive emission has the greatest energy?

It depends on the specific decay; gamma photons generally have the greatest energy among these emissions.

What is conserved in a nuclear equation?

Mass number and atomic number must balance on both sides.

What happens to the mass number during alpha decay?

It decreases by 4.

What happens to the atomic number during alpha decay?

It decreases by 2.

What happens to the mass number during beta-minus decay?

It stays the same.

What happens to the atomic number during beta-minus decay?

It increases by 1.

What happens to the mass number and atomic number during gamma decay?

Both stay the same.

What is the general equation for alpha decay?

Parent nucleus → daughter nucleus + ⁴₂He.

What is the general equation for beta-minus decay?

Parent nucleus → daughter nucleus + ⁰₋₁e.

What is the general equation for gamma decay?

Excited nucleus → lower-energy nucleus + ⁰₀γ.

How do you complete a nuclear equation?

Balance the mass numbers and atomic numbers on both sides.

What is the missing particle in ²³⁵₉₂U → ? + ²³¹₉₀Th?

⁴₂He, an alpha particle.

What is the missing nucleus in ²²⁶₈₈Ra → ⁴₂He + ?

²²²₈₆Rn, radon-222.

What is the order of electromagnetic radiation from lowest to highest energy?

Radio waves, microwaves, infrared, visible light (red to violet), ultraviolet, X-rays, gamma rays.

How does photon energy change as frequency increases?

Energy increases.

How does photon energy change as wavelength increases?

Energy decreases.

What is the formula relating the speed of light, frequency, and wavelength?

c = fλ.

What is the speed of light?

3.00 × 10⁸ m/s.

How do you calculate frequency from wavelength?

f = c ÷ λ.

How do you convert nanometers to meters?

Multiply by 10⁻⁹.

What is the frequency of blue light with a wavelength of 450 nm?

Approximately 6.67 × 10¹⁴ Hz.

What is the frequency of microwaves with a wavelength of 0.125 m?

f = (3.00 × 10⁸) ÷ 0.125 = 2.40 × 10⁹ Hz.

What is a photon?

A packet of electromagnetic energy.

What is the relationship between wavelength and frequency?

They are inversely proportional: as wavelength increases, frequency decreases.

What did Bohr’s atomic model propose?

Electrons occupy specific energy levels.

Why does an element have an emission spectrum with specific colored lines?

Electrons release specific amounts of energy as light when they move to lower energy levels.

What happens when an electron moves to a higher energy level?

It absorbs energy.

What happens when an electron moves to a lower energy level?

It releases energy as a photon.

Which transition emits higher-frequency light: n = 4 to n = 3 or n = 4 to n = 2?

n = 4 to n = 2, because the energy difference is greater.

What is monochromatic light?

Light consisting of one wavelength or frequency.

What is the Aufbau principle?

Electrons fill the lowest-energy orbitals first.

What is Hund’s rule?

Electrons fill orbitals of equal energy singly before pairing.

What is the Pauli exclusion principle?

An orbital holds at most two electrons with opposite spins.

According to the Pauli principle, what is true of two electrons in the same 2s orbital?

They must have opposite spins.

How many electrons can one orbital hold?

Two.

How many orbitals are in a p subshell?

Three.

How many electrons can a p subshell hold?

Six.

How many orbitals are in a d subshell?

Five.

How many electrons can a d subshell hold?

Ten.

How many electrons can an s subshell hold?

Two.

How many electrons can an f subshell hold?

Fourteen.

How do you draw a p orbital diagram?

Draw three boxes side by side, representing three orbitals.

How do you draw a 2p⁴ orbital diagram using Hund’s rule?

[↑↓] [↑] [↑].

Why does 2p⁴ have one paired orbital and two singly occupied orbitals?

Hund’s rule requires each orbital to receive one electron before pairing begins.

How many unpaired electrons are in a 2p⁴ configuration?

Two.

How many unpaired electrons are in a 2p³ configuration?

Three.

How many unpaired electrons are in a 2p⁶ configuration?

Zero.

How many unpaired electrons are in a ground-state phosphorus atom?

Three; phosphorus has a 3p³ configuration.

What is wrong with placing two electrons with the same spin in one orbital?

It violates the Pauli exclusion principle.

What is wrong with pairing electrons in a p subshell before each orbital has one electron?

It violates Hund’s rule.

Why does the 4s orbital fill before the 3d orbital in the usual filling order?

The Aufbau principle says lower-energy orbitals fill first.

What is the usual order of orbital filling?

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s.

What is wrong with the configuration 1s² 2s² 2p⁷?

A p subshell can hold a maximum of six electrons.

What is wrong with an orbital diagram that leaves 1s empty but fills 2s?

It violates the Aufbau principle.

What is the maximum number of electrons in the 3p subshell?

Six.

What is the maximum number of electrons in the 4d subshell?

Ten.

What is an electron configuration?

A notation showing how electrons are distributed among an atom’s energy levels and subshells.

How do you find the number of electrons in a neutral atom before writing its configuration?

Use the element’s atomic number.

What does the superscript in an electron configuration represent?

The number of electrons in that subshell.