Matter, Pure Substances and Mixtures

Matter

• Matter has mass and volume, meaning it takes up space.

Pure Substances vs. Mixtures

• Pure substances result from a chemical change, while mixtures result from a physical change.
• Pure substances include elements and compounds.
• Mixtures include homogeneous and heterogeneous mixtures.

Elements

• Elements consist of only one type of atom.
• Examples include Na (sodium), K (potassium), Ca (calcium), and O (oxygen).

Compounds

• Compounds are combinations of elements.
• Examples include H2O (water), NaCl (sodium chloride), and O2 (oxygen).

Homogeneous Mixtures

• Homogeneous mixtures look the same throughout.
• Examples include milk, pop, and syrup.

Heterogeneous Mixtures

• Heterogeneous mixtures look different throughout.
• Examples include chili, cereal, and bread.

Chemical Change

• A chemical change occurs when a substance combines with another to form a new substance, rearranging the atoms..
• This process can create compounds or release an element from a pre-existing compound.
• Chemical changes are usually irreversible.
• Chemical changes usually involve one or more of the "Big 4" indicators.
• The "Big 4" indicators of a chemical change include:
  • Heat or light being given off (e.g., Mg + O → MgO).
  • Bubbles being formed (e.g., Zn + HCl → ZnCl + H).
  • A precipitate forming (ppt) (e.g., Pb(NO3)2 + KI → PbI2 + KNO3).
  • A color change occurring.

Physical Change

• A physical change affects the form of a chemical substance, but not its chemical composition; atoms are not rearranged.
• The substance remains the same chemical substance, just in a different form.
• Physical changes are usually reversible
• Physical changes do NOT involve any of the "Big 4" indicators

"Tricky" Physical Changes

• Changes of state (e.g., ice, steam, and water are all H2O).
• Dissolving (e.g., making iced tea changes color, but is not a chemical change unless one of the Big 4 happens).
• Bending or breaking (e.g., a smashed cup is still glass).

Physical vs Chemical Properties

• A physical property describes a substance's characteristics without changing its chemical identity.
• A chemical property describes how a substance behaves as it transforms into a new substance through interaction with another substance.

Atomic Structure

• Atoms contain electrons, protons, and neutrons.

Electrons

• Electrons are negatively charged particles orbiting the nucleus
• They have almost no mass.

Protons

• Protons are positively charged particles located in the nucleus of an atom.
• They contribute approximately half of the mass of an atom.

Neutrons

• Neutrons are neutral particles located in the nucleus (with protons) of an atom.
• They contribute approximately half of the mass of an atom.
• Atoms are neutral because they have equal numbers of protons and electrons.

Periodic Table

• The modern periodic table is organized by elements' atomic number.
• Elements are listed from left to right and top to bottom by atomic number.
• Chemical symbols represent each element (e.g., H for hydrogen, Co for cobalt, Na for sodium).

Atomic Number

• An element's atomic number is the number of protons in the nucleus of an atom of that element.
• The atomic number defines the element.
  • For example, an atom with one proton has an atomic number of 1 and is hydrogen.
  • An atom with 11 protons has an atomic number of 11 and is sodium (Na).

Atomic Mass

• Atomic mass is the average mass of one atom of the element.
• It primarily comes from the protons and neutrons in the nucleus; electrons' mass is negligible.

Determining Number of Neutrons

• The number of protons equals the number of electrons in a neutral atom.
• The atomic number equals the number of protons and the number of electrons.
• To find the number of neutrons, subtract the atomic number from the atomic mass.

Standard Atomic Notation

• Notation is as follows:
  • Symbol C
  • Atomic Mass 35
  • Atomic Number 17
• Number of Neutrons is Atomic Mass – Atomic Number, or 35 – 17 = 18 Neutrons

Chemical Formulas

• Chemical formulas use combinations of symbols to represent compounds.
• The formula indicates the elements present and their proportions.
  • For example, one molecule of H2O has 2 hydrogen atoms and 1 oxygen atom.
• If there is only one atom of an element, no number is included.
• If there is more than one atom of an element, the symbol is followed by a subscript.
• A coefficient in front of a compound indicates the number of molecules present.
  • For example, 2 H2O means there are 2 molecules of H2O.

Electron Shells

• 1st Shell: can hold a maximum of of 2 electrons
• 2nd Shell: can hold a maximum of 8 electrons.
• 3rd Shell: can hold a maximum of 8 electrons

Valence Shell

• The valence shell is the outermost shell used by an atom.
• May be the 1st, 2nd, or 3rd shell if it's the outermost shell with the last electron.

Stable Atoms

• A valence shell that is "plump full" of electrons is considered stable.
• Noble gases are the only atoms that are naturally stable.
• Non-noble elements can gain or lose electrons to become stable.

Ions

• An atom that gains electrons becomes negatively charged and turns into a negative ion.
• An atom that loses electrons becomes positively charged and turns into a positive ion.
• An ion is a charged atom

Atoms vs. Ions

• Atoms are neutral (protons = electrons).
• Ions are charged (positive or negative).
• Atoms (except noble gasses) arent stable
• Ions are stable because they have a filled valence shell by gaining or losing electrons.

Isotopes

• An isotope is an element with the same number of protons but a different number of neutrons, resulting in different atomic masses.