Atoms and Atomic Structure

Definition and Arrangement

An atom is the smallest particle of an element that retains the properties of that element. Atoms are composed of subatomic particles arranged in a specific structure.

• Nucleus: The central part of the atom containing protons and neutrons.

• Proton: A positively charged particle found inside the nucleus.

• Neutron: A particle found in the nucleus with no charge (neutral).

• Electron: A negatively charged particle that orbits the nucleus in energy levels.

Example: The carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Energy Levels

Electrons travel around the nucleus in regions called energy levels or shells. Each energy level can hold a specific maximum number of electrons:

• First energy level: can hold up to 2 electrons

• Second energy level: can hold up to 8 electrons

• Third energy level: can hold up to 18 electrons

All energy levels being used must be full for an atom to be stable.

Example: An atom with 8 electrons will have 2 in the first level and 6 in the second level.

Electron Configuration Examples

• Atom with 10 electrons: 2 in the first level, 8 in the second level (stable configuration).

• Atom with 16 electrons: 2 in the first level, 8 in the second, 6 in the third (not fully stable).

Elements and the Periodic Table

Definition and Properties

An element is a substance that cannot be broken down into simpler substances by chemical means. There are 90 naturally occurring elements, all listed on the Periodic Table.

• Only 25 elements are essential for living things.

• 96% of the mass of a human is composed of carbon (C), hydrogen (H), nitrogen (N), and oxygen (O).

Atomic Number and Atomic Mass

• Atomic Number: The number of protons in the nucleus of an atom. It is also equal to the number of electrons in a neutral atom.

• Atomic Mass: The sum of protons and neutrons in the nucleus.

Formula:

Example: Carbon has atomic number 6 and atomic mass 12, so it has 6 neutrons.

Ions and Isotopes

Ions

Ions are charged particles formed when atoms gain or lose electrons. The number of protons does not change.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

Example: has 11 protons and 10 electrons.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Carbon-12: 6 protons, 6 neutrons

• Carbon-13: 6 protons, 7 neutrons

• Carbon-14: 6 protons, 8 neutrons

How Elements Combine: Compounds and Molecules

Compounds

A compound is a substance made of two or more different elements bonded together.

• Example: Sodium chloride (NaCl), Water (H2O)

Molecules

A molecule is a group of atoms held together by covalent bonds.

• Example: Oxygen molecule (O2)

Chemical Bonds

Covalent Bonds

Covalent bonds form when two atoms share electrons. These are common in organic compounds.

• Example: Water (H2O)

Polar and Nonpolar Bonds

• Polar Bond: Electrons are not shared equally, resulting in partial charges on atoms. Example: Water (H2O)

• Nonpolar Bond: Electrons are shared equally. Example: Hydrogen gas (H2), Ethane (C2H6)

Ionic Bonds

Ionic bonds form when atoms transfer electrons, resulting in oppositely charged ions that attract each other.

• Example:

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom in one molecule and an electronegative atom (like oxygen) in another molecule. These bonds are important for holding water molecules and large biological molecules together.

• Example: Hydrogen bonds between water molecules

Properties of Water

Polarity

Water is a polar molecule due to the uneven distribution of charge. Oxygen has a stronger pull on electrons than hydrogen, making the oxygen side slightly negative and the hydrogen side slightly positive.

Cohesion and Adhesion

• Cohesion: Attraction between molecules of the same substance (water molecules stick together).

• Adhesion: Attraction between molecules of different substances (water sticks to glass, causing a meniscus and capillary action).

High Specific Heat Capacity

Water can absorb large amounts of heat due to its many hydrogen bonds, helping regulate temperature in organisms and environments.

Evaporative Cooling

As water evaporates, it removes heat, cooling surfaces (e.g., sweating).

Versatile Solvent

Water dissolves many substances due to its polarity, making it an excellent solvent in biological systems.

Solutions, Acids, and Bases

Solutions

A solution consists of a solute (substance dissolved) and a solvent (substance doing the dissolving). Water is often the solvent in biological systems.

• Example: Iced tea mix (solute) dissolved in water (solvent)

pH Scale

The pH scale measures the concentration of hydrogen ions (H+) versus hydroxide ions (OH-) in a solution. The scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Acid: More H+ ions, pH below 7 (e.g., soda, pH 3)

• Base: More OH- ions, pH above 7 (e.g., Nair, pH 13)

• Neutral: Equal H+ and OH- ions (pure water, pH 7)

Chemical Equations

Reactants and Products

Chemical equations show how substances (reactants) combine to form new substances (products).

Example:

• Reactants: Substances that start the reaction

• Products: Substances formed by the reaction

Coefficients and Subscripts

• Coefficients: Numbers before elements/compounds indicating how many molecules are involved (e.g., 6CO2 means 6 molecules of CO2).

• Subscripts: Numbers within chemical formulas indicating the number of atoms in a molecule (e.g., O2 means 2 oxygen atoms).

Summary Table: Atomic Particles

Summary Table: Types of Chemical Bonds

Additional info: Some context and examples have been expanded for clarity and completeness.