Chemistry Unit 1 and 2 Test

Atom

Smallest unit of matter. Has protons, neutrons, electrons.

Element

Pure substance made of only one type of atom.

Compound

Pure substance of 2+ different elements chemically bonded.

Molecule

Group of atoms bonded together (can be same element or different).

Pure substance

Either an element or a compound, has fixed composition.

Mixture

Physical combo of substances, no fixed ratio.

Homogeneous mixture

Uniform (ex: salt water).

Heterogeneous mixture

Not uniform (ex: oil + water).

Physical properties

Observed without changing substance (melting point, density, color).

Chemical properties

Observed by changing substance (flammability, reactivity).

Physical changes

Doesn't change identity (melting, cutting, dissolving).

Chemical changes

New substance formed (burning, rusting, reacting).

Intensive properties

Don't depend on amount (density, boiling point).

Extensive properties

Depend on amount (mass, volume).

Phase diagram

Graph of pressure vs. temperature showing states of matter.

Triple point

Temp + pressure where solid, liquid, gas coexist.

Critical point

End of liquid-gas line; above it you can't tell liquid/gas apart.

Democritus

First idea of atom (indivisible).

Dalton

Atomic theory (atoms of same element are identical, atoms combine in whole ratios).

Thomson

Discovered electron, "plum pudding model."

Rutherford

Gold foil → discovered nucleus (dense + positive).

Bohr

Electrons in fixed energy levels (like orbits).

Schrödinger

Electron cloud model (probability regions, not fixed paths).

Chadwick

Discovered neutron.

Atomic number (Z)

# of protons (defines element).

Mass number (A)

Protons + neutrons.

Average atomic mass

Weighted average of isotopes.

Protons

+ charge, in nucleus.

Neutrons

Neutral, in nucleus.

Electrons

- charge, orbit nucleus.

Isotopes

Same element, different # neutrons (different mass).

Ions

Charged atoms (gain/lose electrons).

Cation

Positive ion (lost electrons). (Pawsitive...)

Anion

Negative ion (gained electrons).

Valence electrons

Outer shell electrons → control reactivity.

Periodic table notation

Nuclear notation: A/Z Hyphen notation: Name-mass # (Carbon-12).

Periods

Rows (same # energy levels).

Groups

Columns (same # valence electrons).

Representative elements (Groups 1-2, 13-18)

Show predictable valence trends.

Transition elements (Groups 3-12)

Metals, variable charges.

Alkali metals (Group 1)

Very reactive, 1 valence e⁻.

Alkaline earth metals (Group 2)

Reactive, 2 valence e⁻.

Halogens (Group 17)

Very reactive nonmetals, 7 valence e⁻.

Noble gases (Group 18)

Inert, full valence shell.

Rare earth elements

Lanthanides + actinides.

Post-transition metals

Softer, lower melting points (ex: Al, Pb).

Metals

Shiny, malleable, conductors.

Nonmetals

Dull, brittle, poor conductors.

Metalloids

Have properties of both (ex: Si, As).

Mendeleev

Made first periodic table, arranged by atomic mass → predicted missing elements.

Coulombic attraction + Trend

Attraction between + nucleus and - electrons. Stronger when: More protons (higher nuclear charge). Electrons are closer (fewer energy levels).

Electronegativity + Trend

Ability to attract electrons in a bond.

Ionization energy + Trend

Energy needed to remove e⁻.

Atomic radius + Trend

Left and down....

Ionic radius + Trend

Nuclear charge

# protons → effective pull on electrons.

Significant figures

Rules for reporting precision in measurements.

Metallic character

bottom-left strongest.