Compounds and Mixtures Overview

Compounds, Homogenous, and Heterogenous Mixtures

• A compound is formed when two or more elements chemically bond to form a single particle.
• Examples of compounds: Carbon Dioxide (CO2) and Oxygen (O2)
• A homogenous mixture is a uniform mixture of pure substances; all parts are the same.
• Examples of homogenous mixtures: Milk and Oil
• A heterogenous mixture is a non-uniform mixture of pure substances; the parts are unevenly distributed.
• Examples of heterogenous mixtures: Sand + Water, Milk + Nesquik

Metals, Non-Metals, and Metalloids

• Metals:
  • Tend to lose electrons
  • Conduct heat and electricity
  • Malleable (bend into shapes)
  • Ductile (drawn out into wires)
  • Generally solid at room temperature
  • High melting and boiling points
  • Lustrous (shiny)
• Non-Metals:
  • Tend to gain electrons
  • Do not conduct heat and electricity well
  • Brittle (break easily)
  • Not ductile
  • Generally a gas at room temperature
  • Low melting and boiling points
• Metalloids:
  • Have properties of both metals and non-metals
  • Examples: Silicon and Germanium

Atomic Structure and Changes

• Changing the number of protons changes the element.
• Changing the number of electrons changes the charge of an atom, but does not affect the nucleus.
• Changing the number of neutrons changes the stability of the nucleus, creating different isotopes.
• The stability of the nucleus depends on the ratio of protons to neutrons.

Particle Theory

• All matter is made up of particles.
• Particles are attracted to each other.
• When heat is added, particles spread out and move more.
• Particles are always moving.

Density and Water

• Usually, adding heat causes particles to spread out and decrease density.
• Water is an exception because hydrogen bonds form a lattice structure when it freezes, making ice less dense than liquid water.

Ions and Chemical Symbols

• Ions are charged atoms formed by adding or removing electrons.
• Cations are positively charged ions.
• Anions are negatively charged ions.
• Chemical symbols:
  • Generally based on Latin
  • Represents an element
  • Atomic mass is provided below the symbol (average mass of protons and neutrons).

Hydrogen Bonds

• Hydrogen bonds are not actual bonds, but interactions between molecules.
• They occur due to the uneven distribution of electrons in molecules.
• Oxygen has a more negative charge, and hydrogen has a more positive charge.
• This causes a slight attraction between the molecules.
• Hydrogen bonds are responsible for the unique properties of water.

Graphing

• Use a sharp pencil.
• Use a ruler and do not force a curve to be a straight line.
• Have an eraser.
• Do not use “dot to dot” methods for graphing.
• Line graphs are used for continuous data that is usually changing.
• Column graphs are used to compare data.
• Fair test: Only change one variable.
• True validity: Answer the aim and control variables.
• Repeat the experiment for reliable data.