Energy and Matter in Chemical Change — Chapter 1: Atoms, Elements, and Compounds

What is matter?

Matter is anything that has mass and volume; it can be solid, liquid, gas, or invisible like the air you breathe.

What is a mixture?

A combination of two or more substances that can be separated by physical means and does not have a definite composition.

Differentiate a heterogeneous mixture from a homogeneous mixture.

A heterogeneous mixture has visible parts and variable composition; a homogeneous mixture has uniform composition and components are not visibly distinct.

Define an element.

A substance that cannot be chemically broken down into simpler substances.

Define a compound.

Two or more elements chemically combined in definite, fixed proportions.

Define a pure substance.

A substance with a definite composition, including elements and compounds.

What is WHMIS?

The Workplace Hazardous Materials Information System; a Canadian system that provides hazard information, labels, MSDS, and worker education.

State the heart of Dalton’s Atomic Theory.

All matter is made up of atoms; atoms are indivisible and cannot be created or destroyed in reactions; atoms of the same element are identical in mass and size; compounds form when atoms combine in fixed proportions; chemical reactions rearrange atoms.

What evidence supports that matter is made of atoms and that atoms rearrange in reactions?

The law of conservation of mass in reactions and consistent observations that atoms rearrange rather than disappear.

What is an atom?

The basic unit of matter, consisting of a nucleus (protons and neutrons) surrounded by electrons in space.

Who discovered the electron and what was the key idea?

J. J. Thomson discovered the electron; cathode rays are negatively charged particles inside atoms, leading to the plum-pudding model.

Describe Rutherford’s gold foil experiment and its conclusion.

Most alpha particles pass through the foil, few deflect, and a tiny number bounce back; this indicates a tiny, dense positively charged nucleus and mostly empty space.

What is the nucleus of an atom?

The central region that contains protons and neutrons and holds most of the atom’s mass.

What are protons and neutrons?

Protons are positively charged particles in the nucleus; neutrons are electrically neutral particles in the nucleus.

What is an electron?

A negatively charged subatomic particle located in energy levels surrounding the nucleus; it is much lighter than protons and neutrons.

Define isotopes.

Atoms of the same element that have the same number of protons but different numbers of neutrons, leading to different mass.

How do you identify an isotope using nuclear notation?

Use mass number (A) and atomic number (Z) to denote the isotope; A = protons + neutrons, Z = protons.

How many electrons can the first energy level hold? Second energy level?

First level holds 2 electrons; second level holds 8 electrons.

What did Niels Bohr contribute to atomic theory?

Proposed that electrons occupy specific allowed energy levels and that energy is absorbed or emitted when electrons move between levels; explained hydrogen’s emission spectrum.

What is the modern view of electron arrangement beyond Bohr’s model?

Electrons occupy sublevels within energy levels and are arranged in electron clouds; levels can be subdivided into sublevels with paired electrons.

What is the valence energy level?

The outermost occupied energy level in an atom; its electrons are called valence electrons and largely determine chemical behavior.

What is a Lewis (electron dot) diagram?

A representation of an atom’s valence electrons shown as dots around the element’s symbol; also called an electron dot diagram.

What is an ion and what are cations vs anions?

An ion is an atom with a net electric charge. A cation is positively charged (loses electrons); an anion is negatively charged (gains electrons).

What is an ionic compound?

A compound formed from ions held together by ionic bonds, usually between a metal and a non-metal, forming a crystal lattice.

What is a crystal lattice?

A regular, repeating pattern of ions in an ionic compound.

What is a molecular compound?

A compound formed when non-metals share electrons to form molecules via covalent bonds.

What is a covalent bond?

A chemical bond formed by sharing one or more pairs of electrons between atoms.

What is the octet rule?

Most atoms gain, lose, or share electrons to achieve a full outer shell of eight electrons (stable octet).

Give examples of diatomic molecules.

H2, N2, O2, F2, Cl2, Br2, I2 are diatomic molecules common in chemistry.

What are noble gases and why are they often unreactive?

Noble gases (group 18) have a full outer energy level, making them very unlikely to form chemical bonds.

Why do atoms form ions to achieve stability?

By gaining or losing electrons, atoms can achieve the electron configuration of the nearest noble gas, lowering energy and becoming more stable.

How is the electron dot diagram used to predict bonding?

By counting valence electrons, you can predict how many bonds an atom can form and whether bonding will be ionic (transfer) or covalent (sharing).

How do you determine neutrons in an isotope?

Neutrons = mass number (A) minus atomic number (Z).

What is the relationship between atomic number and element identity?

The atomic number equals the number of protons and uniquely identifies the element.

What is the charge and arrangement of ions in sodium chloride (NaCl)?

Sodium forms Na+ (cation) by losing one electron; chlorine forms Cl− (anion) by gaining one electron; they arrange in a crystal lattice with ions in noble-gas-like configurations.

What are the three common ways atoms achieve a full outer shell when forming compounds?

Metal atoms may lose electrons to form cations; non-metals may gain electrons to form anions; or non-metals may share electrons through covalent bonds.

What displays the pattern of electron arrangements across periods and groups?

The periodic table; periods show energy level filling, groups show similar valence electron configurations and chemical properties.

What are the three major sections of the periodic table and the properties they describe?

Metals (shiny, good conductors, malleable), metalloids (border the staircase line with mixed properties), non-metals (poor conductors, dull, brittle).

What is atomic mass and why is it important for isotopes?

Mass number is protons plus neutrons; isotopes have different mass numbers but the same number of protons, affecting overall mass.

What WHMIS symbol is for explosions/reactivity hazards?

Exploding bomb

What WHMIS symbol is for gases under pressure?

Gas cylinder

What WHMIS symbol is for serious health effect hazards?

Health hazard

What WHMIS symbol is for toxins/diseases hazards \?

Biohazard

What WHMIS symbol is for fire hazards?

Flame symbol

What WHMIS symbol is for oxidization hazards?

O-flame symbol

What WHMIS symbol is for damage to metals/skin hazards?

Corrosion

What WHMIS symbol is for acute toxicity?

Skull and crossbones

What WHMIS symbol is for mine health effects or ozone damage?

Exclamation mark