Ch+2-module 2

Matter: Anything that takes up space and has mass, existing in three states: solids, liquids, or gases.
Composed of elements, which are pure substances that cannot be broken down further and possess distinct properties.
Each element has:
- A unique name
- A 1-2 letter abbreviation known as an atomic symbol.
Elements can exist independently or combine to form molecules and compounds.
CHNOPS refers to the most common elements in living organisms:
- C: Carbon
- H: Hydrogen
- N: Nitrogen
- O: Oxygen
- P: Phosphorus
- S: Sulfur
Some elements are necessary only in trace amounts.

Elements are made up of atoms, the smallest unit maintaining the properties of the element.
Atoms consist of three main subatomic particles:
- Protons: Positively charged particles.
- Neutrons: Neutral particles (no charge).
- Electrons: Negatively charged particles.

Protons determine the identity of an atom.
Located in the nucleus of the atom.
The total number of protons defines the atomic number, indicated as a subscript next to the atomic symbol.
In the periodic table, this number appears above the element symbol.
Contributes to atomic mass, with each proton weighing about 1 atomic mass unit.

Neutrons are located in the nucleus and also contribute to atomic mass, weighing about 1.
Do not affect the atomic identity or chemical properties.
Varying numbers of neutrons in the same element result in isotopes.
Some isotopes are unstable and emit energy, termed radioactive isotopes.

Electrons influence an atom's chemical properties.
Their arrangement affects bonding and follows the octet rule, where atoms strive for full outer shells.
Electrons are arranged in shells/energy levels around the nucleus:
- The inner shell can hold a maximum of 2 electrons.
- Subsequent shells can accommodate up to 8 electrons.
Electrons fill the inner shells first before additional shells are considered.

An ordered display presenting:
- Each element's symbol
- Atomic number
- Atomic mass.
Organized in periods (rows) and groups (columns).
Elements in the same period share the same number of electron shells.
Elements in the same group possess similar outer shell electron configurations, leading to similar chemical reactions.

Create atomic diagrams by:
- Placing the atomic symbol in the center as the nucleus.
- Adding the atomic mass and number as superscript and subscript, respectively.
- Representing electrons in shells with dots according to their arrangement.

Atoms form molecules (groups of two or more atoms bonded together) and compounds (two or more different atoms bonded).
Atoms bond to fulfill the octet rule for stability.
Bonds contain energy and allow organisms to utilize this energy for life processes.

Bonding behavior can be inferred from the electron configuration of an element’s outer shell.
Besides H and He, most elements need 8 electrons in their outer shell for stability.
Atoms may share multiple electron pairs, forming single, double, or triple bonds (e.g., methane and oxygen gas).

Electronegativity affects how atoms interact with electrons, leading to transfers.
When electrons transfer, ions with opposite charges form.
The electrostatic attraction between these charged ions creates ionic bonds.

In covalent bonds, atoms share electron pairs.
Sharing can be equal (nonpolar bonds) or unequal (polar bonds), leading to molecular polarity.

In polar molecules, hydrogen bears a slight positive charge, attracting nearby negatively charged areas (like oxygen in water).
Water’s polarity enables extensive hydrogen bonding crucial for biological structures and functions.

Water exhibits several essential properties due to its polarity and hydrogen bonding:
- High heat capacity: Requires significant energy to raise temperature, stabilizing cells' environments.
- High heat of vaporization: Evaporative cooling helps organisms regulate temperature.
- Solvent properties: Dissolves many substances due to being polar, categorizing substances as hydrophilic (water-attracting) or hydrophobic (water-repelling).
Cohesion and adhesion contribute to phenomena like water transportation in plants and surface tension.
Ice's lower density allows it to float, insulating aquatic life below in colder climates.

Water can dissociate into ions:
- Acids release H+ ions.
- Bases absorb H+ or release OH- ions.
pH measures acidity or basic level in a solution.
Buffers are critical in stabilizing pH to maintain biological function in cells.