Chemistry Quiz #2

What is an element?

a substance that cannot be broken down into simpler chemical substances

How many elements are there?

• 90 naturally occurring on Earth

• 30 synthetically created

How do you identify an element?

• Name

• Symbol

• Atomic Number

• Mass Number

What are some the more abundant elements common to the universe, earth and humans?

• Hydrogen

• Helium

• Oxygen

• Carbon

• Neon

• Iron

• Calcium

• Nitrogen

• Silicon

• Aluminum 

What are some uniquely abundant elements in humans compared to earth and the universe?

• Oxygen

• carbon

• Hydrogen

• Calcium

• Iron

• Aluminum

Dalton’s Postulates

• Atoms are indivisible.

• Identical for each element

• Combined in whole-number ratios

What is an atom?

Smallest part of an element (matter) that retains its identity

What are the subatomic particles?

• Proton

• Neutron

• Electron

Proton

• Charge: positive (+)

• Mass: 1.67 × 10^-24

• Location: Nucleus

Neutron

• Charge: 0

• Mass: 1.67 × 10^-24

• Location: Nucleus

Electron

• Charge: negative (-)

• Mass: 9.11 × 10^-28

• Location: Electron Cloud

How do you find the # of electrons?

= to the # of protons

Number of protons - charge

How do you find the atomic number?

It is equal to the number of protons

How do you find the mass number?

Protons + Neutrons

How do you find out the charge?

Protons - Electrons

What does the following indicate: 2H

Two H atoms

What does the following indicate: H₂

One H₂ Molecule

How do you find the # of neutrons?

Atomic # - Mass #

What is an isotope?

Atoms with the same # of protons, but different # of neutrons

What is atomic mass and its unit?

• Weighted average of isotopes

• Unit = amu

Electron Arrangement

• Quantum Mechanics: Electrons have quantized energies.

• Shells: Labeled by n (1, 2, 3...).

• Subshells: s, p, d, f → hold 2, 6, 10, 14 e^- respectively.

• Electron Configuration: Shows distribution (ex: O: 1s² 2s² 2p⁴).

• Valence Electrons = outermost, responsible for bonding

How is the periodic table classified?

• Metals: shiny, conductors, malleable.

• Nonmetals: dull, brittle, poor conductors.

• Metalloids: intermediate properties.

How is the periodic table organized?

• Organized by atomic number & electron configuration.

• Groups = columns (same valence e^- → similar chemistry) 18 groups, up & down

• Periods = rows, 7 periods, # of electron shells, left to right

What are the atomic radius trends?

• Increases ↓ a group (more shells).

• Decreases → across a period (greater nuclear pull).

What is an ionic bond?

Electron transfer (metal + nonmetal)

What is a covalent bond?

Electron sharing (nonmetal + nonmetal)

What is the octet rule?

Atoms stable with 8 valence e^- (duet rule for H, He, Li).

What is a cation?

Loses e^-, positive (metals, left side of table)

What is an anion?

Gains e^-, negative (nonmetals, right side

What is an isoelectronic?

Two ions of the same element with the same electron configuration (ex: Na⁺ and Ne) (same # of electrons)

How do you solve for the average atomic mass?

(# amu × %) + (# amu × %) + (# amu × %)

_________________________________ = amu

100

Atoms on the ______ of the periodic table tend to lose electrons. (<4 v.e.)

Left

Atoms on the _______ of the periodic table tend to gain electrons. (>3 v.e.)

Right

Lewis Diagrams

• Show only valence electrons as dots.

• Pairing begins after each side has 1 electron.

• Arrows represent e⁻ transfer.

Charge Balance

• Compounds must be neutral overall.

• Example: Mg²⁺ + 2 Br⁻ → MgBr₂

Conventions Formula 

1. Cation first.

2. Lowest whole-number ratios.

3. Subscripts used as needed.

Cross-Charges Method Formula

Swap charges to subscripts (Na⁺, O²⁻ → Na₂O)

What are polyatomic ions?

Covalently bonded atoms acting as one charged unit (ex: SO₄²⁻, NH₄⁺)

Ion Naming Rules (CATION)

• Fixed charge: just name (Na⁺ = sodium ion).

• Variable charge: Roman numeral (Fe³⁺ = iron (III) ion).

• Common system: -ic (higher), -ous (lower) (Fe³⁺ = ferric)

Ion Naming Rules (ANIONS)

Add “-ide” (Cl⁻ = chloride, O²⁻ = oxide

Ion Naming (IONIC COMPOUNDS)

Cation name + anion name (NaCl = sodium chloride)

What is an ion?

An atom with a net electric charge 

How do ions form?

When electrons are given to or take from an atom