Chemistry: Matter, Measurement, and Properties

• Chemistry puts the "cation" in education.

Learning Outcomes

• Define matter, mass, weight, volume, and density.
• Describe measurement in chemistry including significant figures when using the scientific method.
• State matter's properties and classifications.
• Outline basic methods for separation and purification.

Foundations of Chemistry

• Chemistry studies matter and its changes.
• Matter is anything that occupies space and has mass
• Matter is classified by its physical state and composition.
• Physical states of matter:
• Gaseous
• Liquid
• Solid

Classification by Physical State

• Solid:
• Has a fixed shape and volume; is rigid.
• Cannot be compressed.
• Particles vibrate and rotate at fixed positions
• Liquid:
• Has a fixed volume.
• Takes the shape of its container.
• Cannot be compressed.
• Particles vibrate, rotate, and translate.
• Gas/Vapor:
• No fixed volume or shape conforming to the container.
• Can be compressed or expanded.
• Moves randomly at high speeds
• Particles can vibrate, rotate, translate, and have high energy content.

Physical vs. Chemical Change

• Physical change does not alter the composition or identity of a substance.
• For example, ice melting and sugar dissolving in water.
• Chemical change alters the composition or identity of a substance.
• For example, hydrogen burning in air to form water.

Matter Classification Based on Composition

• The pure substances are compounds and elements
• Mixtures can be either homogenous or heterogenous

Basic Element Differences

• Element:
• Contains only one kind of atom.
• Cannot be broken down.
• Compound:
• Consists of atoms of two or more different elements.
• Can be broken down.
• Mixture:
• Consists of two or more different elements/compounds.
• Can be separated.

Element Categories

• Elements are classified as either a metal or a non-metal

Chemical Separations: Compounds

• Electrolysis is used to separate compounds (pure substances).
• Electrolysis does not involve a physical separation.
• Electrolysis is a chemical separation using electricity.
• This process separates water into hydrogen and oxygen.

Mixture Separation Based on Composition

• Mixtures contain two or more elements/compounds, physically combined.
• Mixtures are seperated by physical methods
• Separated by distillation, crystallization, evaporation, filtration, centrifugation, fractional distillation, sublimation, chromatography, magnetism, and extraction.
• Components of a mixture retain individual identities.
• Mixtures can be homogenous or heterogenous.
• Homogenous mixtures have the same composition throughout
  • Example: soft drink, milk
• Heterogenous mixtures have a composition that is not uniform
  • Example: cement, iron filings in sand

Separating Mixtures

• Magnetism: Use a magnet to separate the mixture if one component has magnetic properties.
• Iron, nickel, and cobalt are magnetic.
• Gold, silver, and aluminum are not magnetic.
• Filtration: Used to separate a solid substance from a liquid or gas.
• A mix is put through a porous material like a filter.
• Fluid passes through, but the solid is kept out.
• Coffee and oil filters work on this principle.
• Centrifuging: This method requires the materials of the mixture to have varied densities.
• Spinning a sample rapidly causes Denser materials to settle at the bottom.
• This method is used with blood to separate it into serum and plasma.
  • Serum (clear)
  • Plasma (has RBC)
  • Useful to check for anemia (lack of iron)
• Decanting: Used for immisicble liquids like water and oil mix
• The mix is poured into a separating tunnel and shaken
• Shaking the tunnel and allowing it settle will cause the layers to distinct
• The denser layer will form the bottom layer
• Chromatography: A series of techniques separate a complex of substances as different components of the mixture travel at variable speeds,
• Some substances dissolve better in the liquid better, thus traveling further up the paper compared to others
• Components with the strongest attraction for the chromatography paper travel the slowest
• Distillation: A method to separate a liquid from a solution.
• Used to separate liquid from liquid (alcohol from water) / solids from liquids (water from salts), since the substances have differing boiling points
• Crystallization: A separation technique that results in creating pure solid particles from a solution containing dissolved substances
• As the solvent evaporates, the dissolved subs comes out of solution.
• Water/solvent= evaporates, not the solution
• Produces highly pure solids
  • Examples: rocky candy

Units

• Mass:
• Measures the quantity of matter.
• SI unit is the kilogram (kg).
• 1 kg = 1000 g =1 x 10^3g
• Weight:
• A force of gravity exerted on an object.

International System of Units (SI)

Prefixes Used With SI Units

• Volume:
• The SI derived unit for volume is the cubic meter (m^3).
• 1 cm³ = (1 x 10⁻² m)³ = 1 x 10⁻⁶ m³
• 1 dm³ = (1 x 10⁻¹ m)³ = 1 x 10⁻³ m³
• 1 L = 1000 mL = 1000 cm³ = 1 dm³
• 1 ml = 1cm^3
• Density:
• The Sl derived unit for density is kg/m³.
• 1 g/cm³ = 1 g/mL = 1000 kg/m³
• density = mass/volume
• d = m/v

Temperature Conversions

• K = °C + 273.15
  • 273.15 K = 0°C
  • 373.15 K = 100°C
• °F = (9/5) x °C + 32
  • 32 °F = 0°C
  • 212 °F = 100°C

Atom Basics

• Atom - the smallest part of an element that can take part in chemical changes.
• Usually individual atoms are not found in nature except for noble gases (He, Ne, Ar... Xe) which occur in atomic form.

Molecule Basics

• Molecule - the smallest particle of a substance that still has the properties of that substance.
• Several elements exist as diatomic molecules:
• H₂ - Used as fuel and in small weather balloons.
• O₂ - Vital to sustain life and essential for combustion.
• N₂ - Most abundant in the atmosphere, used as inert gas and to generate ammonia.

Dalton's Atomic Theory

• All matter consists of atoms, which are tiny particles that cannot be created, destroyed or split
• Atoms are the smallest unit of an element
• All atoms of a given element are identical in all aspect (size, mass, chemical properties)
• The atoms of one element are different from the atoms of all other elements
• Compounds are composed of atoms of more than one element combined in a fixed simple ratio

Atomic Structure

• An atom / an isotope can be represented using this format:
  • Mass number is on top left - (#protons+#neutrons)
  • Atomic number is on botton left -(#protons)
• Atomic number = proton number
• Nucleon number / mass number (A) = total no. of protons & neutrons
• A = Z + N (no. of neutrons)

Isotopes

• Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons/(different no. of nucleon/mass number)
• Although the masses of the isotopes are different, they behave similarly chemically.

Key Terms

• Atom: The smallest unit of matter that can have the properties of an element.
• Compound: A molecule containing two or more different atoms bound together.
• Element: A fundamental substance that has a unique atomic number on the periodic table.
• Gas: A form of matter with mass but no definite shape, and that can be either compressed or expanded to fill an infinite volume.
• Isotope: A different form of an element that varies by the number of neutrons in the nucleus.
• Liquid: A form of matter that has mass, occupies a volume, and flows to adopt the shape of its container.
• Solid: A form of matter a with definite shape and volume.

Measurements

• Atomic Mass: The mass of an atom (protons, neutrons, electrons).
• Relative Atomic Mass: An element's atomic mass relative to the mass of a carbon-12 atom.
• Carbon-12 atom = 1.992 × 10-23 g
• atomic mass unit (amu) = 1/12 the mass of a 12Carbon atom 1 p = 1.007276 amu 1 n = 1.008665 amu 1 e = 0.0005486 amu

Mass Spectrometry

• The relative mass of atoms can be determined by mass spectrometry.
• A mass spectrometer is used to measure the:
• Relative atomic mass.
• Relative molecular mass.
• Relative isotopic mass.
• Structural formula of compounds.

Average Atomic Mass

• Isotopes are atoms of the same element that have different numbers of neutrons.
• The relative atomic mass of an element is the average value for the isotopes of the element.
• To calculate this, you have to take into account the percentage abundance of the isotopes.

Ions

• A charged particle.
• Electrons are not equal in amount to the protons.
• Ionization occurs when electrons are lost or gained.
• Cations:
• Positively charged ions.
• Elements in groups 1, 2, & 3 lose electrons to form cations.
• Metal cations with more than one oxidation state have Roman numerals
• Anions:
• Negatively charged ions.
• Atoms gain an electron (in the valence shell) to form anions.
• Salts:
• A compound formed when the negative ions from an acid combine with the positive ions of a base, via ionic bond.