States and Properties of Matter, Atomic Structure, and Electron Configuration – GOB Chemistry Study Notes (Week 2)

States and Properties of Matter

Introduction to States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state is characterized by distinct physical properties and particle arrangements.

• Solid: Definite shape and volume; particles are closely packed in a fixed arrangement and move very slowly.

• Liquid: Indefinite shape but definite volume; particles are close together but mobile, moving slowly.

• Gas: Indefinite shape and volume; particles are far apart and move very fast.

Comparison of Solids, Liquids, and Gases

The following table summarizes the main differences between solids, liquids, and gases:

Characteristic	Solid	Liquid	Gas
Shape	Definite	Takes shape of container	Takes shape of container
Volume	Definite	Definite	Fills volume of container
Arrangement of Particles	Fixed, very close	Random, close	Random, far apart
Attraction between Particles	Very strong	Strong	Essentially none
Movement of Particles	Very slow	Moderate	Very fast
Examples	Ice, salt, iron	Water, oil, vinegar	Water vapor, helium

Physical Properties of Matter

Physical properties are characteristics that can be observed or measured without changing the identity of a substance. Examples include:

• Shape

• Physical state (solid, liquid, gas)

• Boiling and freezing points

• Density

• Color

Chemical Properties of Matter

Chemical properties describe the ability of a substance to interact with other substances and to change into new substances. Examples include:

• Reactivity with oxygen

• Ability to burn

• Ability to tarnish

Physical and Chemical Changes

A physical change alters the state or appearance of a substance without changing its composition. A chemical change results in the formation of one or more new substances with new properties.

• Physical Change Examples: Melting, boiling, dissolving, cutting, grinding

• Chemical Change Examples: Burning, rusting, tarnishing, caramelizing sugar

Changes of State

Melting and Freezing

Melting is the process by which a solid becomes a liquid at its melting point. Freezing is the reverse process, where a liquid becomes a solid at its freezing point. These are reversible processes.

• Heat of Fusion: The amount of heat required to melt 1 g of a solid at its melting point, or released when 1 g of liquid freezes at its freezing point.

Evaporation, Boiling, and Condensation

Evaporation occurs when molecules at the surface of a liquid gain enough energy to become a gas. Boiling involves molecules throughout the liquid converting to gas. Condensation is the reverse, where gas molecules lose energy and form a liquid.

• Heat of Vaporization: The amount of heat required to convert 1 g of liquid to gas at the boiling point, or released when 1 g of gas condenses to liquid.

Sublimation and Deposition

Sublimation is the direct change from solid to gas without passing through the liquid state. Deposition is the reverse process. These are reversible changes.

• Example: Dry ice (solid CO2) sublimes at -78°C.

Density and Specific Gravity

Density

Density compares the mass of an object to its volume. It is a physical property used to identify substances and predict whether objects will sink or float in water.

• Formula: $\text{Density} = \frac{\text{mass of a substance}}{\text{volume of a substance}}$ Units: g/cm3 or g/mL

• 1 mL = 1 cm3

Calculating Density by Water Displacement

To determine the volume of an irregular solid, submerge it in water and measure the volume displaced.

• Example: If water rises from 25.0 mL to 33.0 mL after adding a 48.0 g metal sample, volume displaced = 8.0 mL. $\text{Density} = \frac{48.0\,\text{g}}{8.0\,\text{mL}} = 6.0\,\text{g/mL}$

Specific Gravity

Specific gravity is the ratio of the density of a substance to the density of water (1.00 g/mL at 4°C). It is a unitless quantity.

• Formula: $\text{Specific gravity} = \frac{\text{density of sample}}{\text{density of water}}$

Atomic Structure

Dalton’s Atomic Theory

Dalton proposed that atoms are tiny particles of matter, each element consists of similar atoms, and atoms of different elements combine to form compounds. Atoms are rearranged in chemical reactions but are not created or destroyed.

Subatomic Particles

Atoms consist of three main subatomic particles:

• Proton: Positive charge (+1), located in the nucleus

• Neutron: No charge (neutral), located in the nucleus

• Electron: Negative charge (-1), located outside the nucleus

Atomic Models

• Thomson’s Plum-Pudding Model: Atoms are composed of electrons scattered within a positively charged cloud.

• Rutherford’s Gold Foil Experiment: Atoms have a small, dense, positively charged nucleus; electrons occupy the space around the nucleus.

Atomic Mass Unit (amu)

The atomic mass unit (amu) is used to express the mass of subatomic particles. 1 amu is approximately the mass of a proton or neutron.

Atomic Number and Mass Number

• Atomic Number (Z): Number of protons in the nucleus; unique for each element.

• Mass Number (A): Total number of protons and neutrons in the nucleus. $\text{Mass number} = \text{number of protons} + \text{number of neutrons}$

• Number of Neutrons: $\text{Number of neutrons} = \text{mass number} - \text{atomic number}$

• In a neutral atom, number of protons = number of electrons.

Isotopes and Atomic Mass

Isotopes are atoms of the same element with different mass numbers due to varying numbers of neutrons. The atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes.

• Example: Carbon has three isotopes: 12C, 13C, 14C.

Electron Energy Levels and Orbitals

Electromagnetic Radiation and Atomic Spectrum

Electromagnetic radiation includes visible light, X-rays, and other forms of energy that travel as waves. The atomic spectrum is unique for each element and results from electrons changing energy levels.

Electron Energy Levels

• Electrons occupy specific energy levels, designated by principal quantum numbers (n = 1, 2, 3, ...).

• Energy increases as n increases; electrons farther from the nucleus have higher energy.

• Energy is quantized; electrons can only have certain energy values.

Sublevels and Orbitals

• Each energy level contains one or more sublevels: s, p, d, f.

• Order of sublevels: s < p < d < f

• Each sublevel contains a specific number of orbitals:

Sublevel	Number of Orbitals	Maximum Electrons
s	1	2
p	3	6
d	5	10
f	7	14

• s orbitals: Spherical shape

• p orbitals: Two-lobed (dumbbell) shape, oriented along x, y, z axes

• d orbitals: Four-lobed shapes, with one having a doughnut ring

Electron Spin and Pauli Exclusion Principle

• Each orbital can hold a maximum of two electrons with opposite spins.

• Electrons in the same orbital must have opposite magnetic spins.

Electron Configuration and Chemical Properties

The arrangement of electrons in energy levels and sublevels determines the chemical and physical properties of elements.

• Example: Elements with electrons in the 3p sublevel include arsenic (As).

Additional info:

• Some context and examples were inferred from standard GOB Chemistry curriculum to ensure completeness and clarity.