Chemistry Basics Quiz

Matter, Atoms, Elements, and the Periodic Table

• Matter has mass and occupies space
• Three forms of matter: solid, liquid, gas
• Atom is the smallest particle exhibiting chemical properties of an element.
• 92 naturally occurring elements make up matter
• Elements are organized in the periodic table.

Most Common Elements in the Human Body

• Oxygen (O): 65.5%
• Carbon (C): 18.5%
• Hydrogen (H): 9.5%
• Nitrogen (N): 3.0%
• Calcium (Ca): 1.5%
• Phosphorus (P): 1.0%
• Other minor elements are less than 1%

Components of an Atom

• Atoms are composed of three subatomic particles: neutrons, protons, and electrons
• Neutrons:
  • Have a mass of one atomic mass unit (amu)
  • Have no charge
  • Located in the nucleus
• Protons:
  • Have a mass of one amu
  • Have a positive charge (+1)
  • Located in the nucleus
• Electrons:
  • Have 1/1800th the mass of a proton or neutron
  • Have a negative charge (-1)
  • Located at varying distances from the nucleus in regions called orbitals or shells

Periodic Table

• Chemical symbol: unique to each element
• Usually identified by the first letter or first letter plus another letter
• Atomic number: number of protons in an atom
• Located above the element symbol
• Average atomic mass: shown below the element symbol on the table
• Elements are arranged by atomic number in rows.

Determining the Number of Subatomic Particles

• Proton number = atomic number
• Neutron number = atomic mass - atomic number
• Electron number = proton number

Diagramming Atomic Structures

• An atom has electron "shells" surrounding the nucleus
• Each shell has a specific energy level
• The innermost shell holds two electrons, the second shell up to eight.
• Shells close to the nucleus must be filled first.

Isotopes

• Isotopes are different atoms of the same element.
• They have the same number of protons and electrons but different numbers of neutrons.
• Identical chemical characteristics but different atomic masses
• Example: Carbon-12, Carbon-13, Carbon-14 (all have 6 protons and 6 electrons but different numbers of neutrons).
• Weighted average of atomic mass for all isotopes gives the average atomic mass for that element.

Radioisotopes

• Contain excess neutrons, making them unstable
• Lose nuclear components as high-energy radiation
• Examples of radiation: alpha particles, beta particles, and gamma rays
• Physical half-life: the time it takes for 50% of a radioisotope to become stable.
• Biological half-life: the time it takes for half the radioactive material to be eliminated from the body.

Chemical Stability and the Octet Rule

• Periodic table organized into periods (horizontal rows) and groups (columns)
• Each column has a similar valence electron configuration.
• Elements in column VIIIA have a full valence shell and are chemically stable (e.g., Helium, Neon).

Ions and Ionic Compounds

• Atoms with a positive or negative charge are called ions
• Ions are formed by atoms gaining or losing electrons
• Ionic compounds are structures formed from positively and negatively charged ions.
• Ions are held together by electrostatic forces in a lattice structure.
• Examples of ionic compounds: table salt (NaCl), magnesium chloride.

Covalent Bonds, Molecules, and Molecular Compounds

• In covalent bonds, atoms share electrons
• Molecules are structures composed of two or more atoms bonded covalently, or a single atom
• Molecular formulas indicate the number and type of atoms in a molecule.
• Structural formulas show how atoms are arranged in a molecule.
• Example molecules: carbon dioxide (CO2), water (H2O)
• Types of bonds: single, double, and triple covalent bonds

Isomers

• Isomers have the same molecular formula but different structural formulas.
• Example: glucose, galactose, fructose (all have the same molecular formula C6H12O6 but different structures)

Nonpolar and Polar Covalent Bonds

• Electronegativity is the relative attraction of atoms for electrons.
• In a covalent bond, unequal sharing creates a polar bond (partial charges).
• Equal sharing creates nonpolar bond (no partial charges).
• Example: Water (H2O) is polar with the oxygen atom having a partial negative charge and hydrogens having a partial positive charge.

Amphipathic Molecules

• Molecules with both polar and nonpolar regions
• Example: phospholipids, which have a polar head and nonpolar tails.

Intermolecular Attractions

• Weak forces between molecules
• Important for the shape and function of larger molecules like DNA and proteins
• Examples: hydrogen bonds, Van der Waals forces
• Hydrophobic interactions: repulsion between nonpolar molecules in a polar solvent.
• Hydrophilic interactions: attraction between polar molecules or ions and water

Water

• Water is a polar molecule with slightly positive hydrogen atoms and slightly negative oxygen atoms.
• Polarity allows water to form hydrogen bonds with other molecules.
• Water's properties: high specific heat, high heat of vaporization, universal solvent, cohesive and adhesive properties, and surface tension.
• Water as a solvent: substances that dissolve readily in water are called hydrophilic ("water-loving"), and those that do not dissolve are hydrophobic ("water-fearing"). Example: water is capable of dissolving ionic compounds such as NaCl, and polar compounds like glucose and alcohol.
• The role of water in biological systems: essential role in solubility, transport, lubrication, and cushions.

pH, Neutralization, and the Action of Buffers

• pH is a measure of hydrogen ion (H+) concentration in a solution.
• Acids release H+ ions into a solution, whereas bases absorb H+ ions.
• Neutralization is the process of returning an acidic or basic solution to neutral pH (typically 7).
• Buffers are substances that help maintain a stable pH by absorbing or releasing H+ ions.

Water Mixtures

• Mixtures are formed from combining two or more substances that are not chemically changed.
• Common types of mixtures: suspensions, colloids, and solutions
• Colloids and suspensions: larger particles, colloids remain mixed but suspensions may settle or require agitation, example Blood
• Solutions: smallest particles, does not scatter light or settle, example water solutions.