Ch2

Matter
- Refers to anything that takes up space and has mass.
- Can exist in three states: solid, liquid, or gas.
- Composed of elements.
Element
- A substance that cannot be broken down into another substance by ordinary chemical means.
- There are 92 naturally occurring elements.
- Four elements that make up about 96% of the body weight of most living organisms:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)

Normal chemical reactions do not produce elements.
Heavier elements, such as iron, are produced during supernova explosions.
Supernovas scatter heavier elements into space, where they eventually become part of planets.
Notably, the iron found in blood originates from these stellar explosions.
Quote by Neil deGrasse Tyson: "After all, what nobler thought can one cherish than that the universe lives within us all?"

Atomic Theory: States that elements consist of atoms.
Atomic Symbol: Represents the name of the atom or element (e.g., H for hydrogen, Na for sodium).
Subatomic Elements:
- Neutrons: No electrical charge, located in the atomic nucleus.
- Protons: Positive charge, also in the nucleus.
- Electrons: Negative charge, found outside of the nucleus, moving in orbitals.
Mass Number: The sum of protons and neutrons (electrons are negligible in mass).
Atomic Weight: This varies with gravitational pull.

Atomic Number: All atoms of an element have the same number of protons.
This also indicates the number of electrons if the atom is electrically neutral.
Periodic Table:
- Elements are organized such that their chemical and physical characteristics recur in a predictable manner.
- Atoms are arranged into periods (rows) and groups (columns).

Isotopes: Atoms of the same element that differ in the number of neutrons.
Isotopes have the same number of protons but a different number of neutrons which results in different mass numbers.
Characteristics:
- Some isotopes are unstable and may decay, emitting radiation.
- They can be used for medical imaging (e.g., PET scans).
- Can cause cellular damage leading to cancer.
- Useful for sterilizing medical equipment.

Electron Configuration: Electrons are in constant motion, and can be modeled with energy levels or electron shells.
The first shell can hold up to two electrons.
Each subsequent shell can hold up to eight electrons.
Octet Rule:
- Valence shell is the outermost shell.
- Stability occurs when the outer shell has eight electrons.
- Atoms can give up, accept, or share electrons to achieve a stable configuration.
- Chemical properties of atoms are primarily determined by the arrangement of their electrons.

Molecule: A group of atoms bonded together (e.g., O2 for oxygen gas, H2O for water).
Compound: A molecule containing atoms of at least two different elements (e.g., NaCl or H_2O).
Ionic Bonds:
- Formed when electrons are transferred between atoms, creating ions.
- Ion: An atom or molecule with an electrical charge due to the loss or gain of electrons.
- Cation: A positively charged ion (loses electrons).
- Anion: A negatively charged ion (gains electrons).
- Occur typically between a metal and a nonmetal.
- The attraction between oppositely charged ions forms the bond (e.g., Na^+ and Cl^- form NaCl).
Covalent Bonds:
- Formed when atoms share electrons to achieve a stable outer shell.
- Can occur between two nonmetal atoms.
- Nonpolar Covalent Bonds: Electrons are shared equally between the atoms (e.g., O2, H2).
- Polar Covalent Bonds: Electrons are shared unequally, resulting in partial positive and partial negative charges on different parts of the molecule (e.g., H_2O). Oxygen is more electronegative than hydrogen, pulling electrons closer to itself.