Midterm 1 Review: Matter, Atoms, Compounds, and Chemical Quantities

Matter and Measurements

Classification of Matter

Matter is anything that has mass and occupies space. It can be classified based on its composition and properties.

• Non-metals: Elements that generally lack metallic properties, are poor conductors, and tend to gain electrons in reactions. Example: Oxygen (O).

• Metals: Elements that are good conductors of heat and electricity, malleable, ductile, and tend to lose electrons. Example: Iron (Fe).

• Elements: Pure substances consisting of only one type of atom. Example: Hydrogen (H).

• Compounds: Substances formed from two or more elements chemically bonded. Example: Water (H2O).

• Homogeneous Mixtures: Mixtures with uniform composition throughout. Example: Saltwater.

• Heterogeneous Mixtures: Mixtures with non-uniform composition. Example: Salad.

• Noble Gases: Elements in Group 18 of the periodic table, known for their lack of reactivity. Example: Neon (Ne).

Particles and Properties

• Cations: Positively charged ions formed by loss of electrons.

• Anions: Negatively charged ions formed by gain of electrons.

• Protons: Positively charged subatomic particles in the nucleus.

• Neutrons: Neutral subatomic particles in the nucleus.

• Electrons: Negatively charged subatomic particles orbiting the nucleus.

• Solids: State of matter with definite shape and volume.

• Liquids: State of matter with definite volume but no definite shape.

• Gases: State of matter with neither definite shape nor volume.

Intermolecular Forces

• Dispersion Forces: Weak forces due to temporary shifts in electron density.

• Hydrogen Bonding: Strong dipole-dipole attraction between H and N, O, or F.

• Dipole-Dipole: Attraction between polar molecules.

Atoms and the Periodic Table

Periodic Table Organization

The periodic table arranges elements by increasing atomic number and groups elements with similar properties.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Periods: Horizontal rows; properties change progressively across a period.

• Noble Gases: Located in Group 8A (18).

Atomic Structure

• Atomic Number: Number of protons in the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Electron Configuration: Arrangement of electrons in an atom.

Element Comparison

• Atomic Size: Increases down a group, decreases across a period.

• Ionization Energy: Energy required to remove an electron; increases across a period.

• Metallic Character: Increases down a group, decreases across a period.

• Electronegativity: Tendency to attract electrons; increases across a period.

Ionic and Molecular Compounds

Naming Compounds

Compounds are named based on the elements present and their ratios.

• Ionic Compounds: Formed from metals and non-metals; named by cation then anion. Example: NaCl (sodium chloride).

• Molecular Compounds: Formed from non-metals; prefixes indicate number of atoms. Example: CO2 (carbon dioxide).

Chemical Symbols

• Symbols: One or two-letter abbreviations for elements. Example: Fe for iron.

• Formulas: Indicate the composition of compounds. Example: H2O for water.

Lewis Dot Structures and Molecular Geometry

Lewis dot structures show valence electrons. Molecular geometry describes the shape of molecules.

Compound	Lewis Dot Structure	Electron Geometry	Molecular Geometry (Shape)	Bond Angles	Polar or non-polar?
O2	O::O	Linear	Linear	180°	Non-polar
CH4	C with 4 H's around	Tetrahedral	Tetrahedral	109.5°	Non-polar
H2S	S with 2 H's and 2 lone pairs	Tetrahedral	Bent	~104.5°	Polar
CO2	O=C=O	Linear	Linear	180°	Non-polar
KF	K+ F-	Linear	Linear	180°	Polar (ionic)

Chemical Reactions & Quantities

Significant Figures

Significant figures reflect the precision of a measurement.

• Leading zeros are not significant.

• Trailing zeros after a decimal are significant.

• All non-zero digits are significant.

Conversions and Calculations

Conversions between units and chemical quantities are essential in chemistry.

• Temperature: $K = ^ ext{o}C + 273.15$

• Moles to atoms: $1 ext{ mole} = 6.022 imes 10^{23} ext{ particles}$

• Molar mass: $ext{mass} = ext{moles} imes ext{molar mass}$

Atoms and Subatomic Particles

Atomic Structure Table

Element Symbol	Number of Protons	Number of Electrons	Atomic Number
Cu	29	29	29
Pt	78	78	78
As	33	33	33
O	8	8	8
Mg	12	12	12
Mn	25	25	25
U	92	92	92

Lab Techniques and Mathematical Operations

Conversions and Calculations

• Use dimensional analysis for unit conversions.

• Always check significant figures in final answers.

• Common conversions: grams to moles, moles to atoms, temperature conversions.

Example Conversion

• To convert 238 K to °C: $^ ext{o}C = K - 273.15$

• To convert moles to atoms: $ext{atoms} = ext{moles} imes 6.022 imes 10^{23}$

Additional info:

• Practice questions cover all major topics for a GOB Chemistry midterm, including atomic structure, periodic table, chemical bonding, molecular geometry, intermolecular forces, naming compounds, and quantitative conversions.

• Students should be familiar with using the periodic table, identifying element properties, and performing basic chemical calculations.