Chemistry Lecture Notes: Key Vocabulary (Elements, Molecules, Ions, Units, and Measurements)

Vocabulary flashcards covering elements, atoms, molecules, ions, polyatomic ions, SI prefixes, units of volume, density, temperature scales, Avogadro’s number, scientific notation, significant figures, exact numbers, and related concepts from the notes.

Element

A substance that cannot be separated into simpler substances by chemical means.

Naturally occurring elements

Elements that occur in nature on Earth (about 82 total).

Synthetic elements

Elements created by scientists in laboratories (e.g., technetium, americium, seaborgium, californium).

Periodic table

A chart showing all known elements arranged by increasing atomic number and grouped by similar properties.

Period

A horizontal row in the periodic table.

Group

A vertical column in the periodic table.

Atomic number

The number of protons in an atom; identifies the element.

Atomic mass

The weighted average mass of an element’s atoms, usually given in atomic mass units.

Element symbol

A one- or two-letter abbreviation for an element (e.g., H, He, Au).

Atom

The basic building block of matter; the smallest unit of an element that retains its identity.

Molecule

A group of two or more atoms held together by covalent bonds.

Homonuclear molecule

A molecule consisting of two or more atoms of the same element (e.g., O2, N2).

Heteronuclear molecule

A molecule containing atoms of two or more different elements (e.g., H2O, CO2).

Compound

A substance made of two or more different elements chemically combined in fixed proportions.

Ion

An atom or group of atoms with a net positive or negative charge.

Cation

An ion with a positive charge.

Anion

An ion with a negative charge.

Monatomic ion

An ion consisting of a single atom.

Polyatomic ion

An ion consisting of two or more atoms.

Nitrate (NO3-)

A polyatomic anion with formula NO3- and a -1 charge.

Carbonate (CO3^2-)

A polyatomic anion with formula CO3^2- and a -2 charge.

Sulfate (SO4^2-)

A polyatomic anion with formula SO4^2- and a -2 charge.

Phosphate (PO4^3-)

A polyatomic anion with formula PO4^3- and a -3 charge.

Hydroxide (OH-)

A polyatomic anion with formula OH- and a -1 charge.

Azide (N3-)

A polyatomic anion with formula N3- and a -1 charge.

Perchlorate (ClO4-)

A polyatomic anion with formula ClO4- and a -1 charge.

Chlorate (ClO3-)

A polyatomic anion with formula ClO3- and a -1 charge.

Chlorite (ClO2-)

A polyatomic anion with formula ClO2- and a -1 charge.

Polyatomic ion

An ion composed of two or more atoms.

Avogadro’s number

6.022 × 10^23 particles per mole.

Scientific notation

A method of writing numbers as a × 10^n, where a is between 1 and 10.

femto (f)

Prefix meaning 10^-15.

pico (p)

Prefix meaning 10^-12.

nano (n)

Prefix meaning 10^-9.

micro (μ)

Prefix meaning 10^-6.

milli (m)

Prefix meaning 10^-3.

centi (c)

Prefix meaning 10^-2.

deci (d)

Prefix meaning 10^-1.

kilo (k)

Prefix meaning 10^3.

mega (M)

Prefix meaning 10^6.

giga (G)

Prefix meaning 10^9.

tera (T)

Prefix meaning 10^12.

Volume (m^3)

Cubic meter; SI derived unit for volume.

Cubic centimeter (cm^3)

Volume equal to 1 mL; 1 cm^3 = 1 mL.

Liter (L)

Unit of volume equal to 1000 cm^3; 1 L = 1000 mL.

Milliliter (mL)

Volume unit equal to 1 cm^3; 1 mL = 1 cm^3.

1 dm^3 = 1 L

One cubic decimeter equals one liter.

1 mL = 1 cm^3

Equivalent volumes used interchangeably.

Density

SI derived quantity: density = mass/volume; units kg/m^3 (commonly g/cm^3 or g/mL).

d = m/V

Formula for density: mass divided by volume.

1 g/cm^3

Common density unit equal to 1 g/mL; equals 1000 kg/m^3.

Temperature scales

Kelvin (K), Celsius (°C), and Fahrenheit (°F) scales.

Kelvin (K)

SI temperature scale; K = °C + 273.15; absolute zero at 0 K.

Celsius (°C)

Temperature scale with water freezing at 0°C and boiling at 100°C at 1 atm.

Fahrenheit (°F)

Temperature scale where water freezes at 32°F and boils at 212°F at 1 atm.

K = °C + 273.15

Conversion formula from Celsius to Kelvin.

F = (9/5)°C + 32

Conversion formula from Celsius to Fahrenheit.

Absolute zero

Lowest possible temperature, 0 K (−273.15 °C).

Significant figures

Digits that carry meaning about a measurement’s precision; rules govern which zeros are significant.

Leading zeros

Zeros to the left of the first nonzero digit; not significant.

Captive zeros

Zeros between nonzero digits; significant.

Trailing zeros with decimal point

Zeros to the right of the decimal point are significant.

Exact numbers

Counts or defined quantities with infinite significant figures; do not limit result’s sig figs.

Scientific notation (practical use)

A method to express very large or very small numbers concisely without long decimals.

Sublimation

Physical change where a solid changes directly to a gas without becoming liquid.

Physical change

A change where the substance alters form or state but not identity.

Chemical change

A change that alters the substance’s identity by forming new substances.