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Chem Review. Experimentation. Scientific method: Problem – ask question Observations Hypothesis – educated guess; improves with experience and prior knowledge Experiment – tests hypothesis MUST be repeatable; reliability, error Steps called procedure; avoid bias

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Scientific method:

  • Problem – ask question
  • Observations
  • Hypothesis – educated guess; improves with experience and prior knowledge
  • Experiment – tests hypothesis
  • MUST be repeatable; reliability, error
  • Steps called procedure; avoid bias
  • MUST consider all control variables (factors that could affect the outcome of experiment) when designing; makes results more valid
  • Affected by accuracy and precision
precision and accuracy
Precision and Accuracy


  • How close measurements are to each other
  • Increases with better measuring equipment
  • Higher resolution (smaller intervals) is better
  • Example: graduated cylinder is better than a beaker, buret is better than a grad cyl
precision and accuracy1
Precision and Accuracy…


  • How close the measurement is to the true value
  • Affected by calibration
  • 2 ways to look at improvement
  • Practice to improve with SAME instrument
  • Choose more precise instrument and automatically improves
  • Measurements should be both accurate and precise
scientific method
Scientific Method

Last two steps:


  • Organize, evaluate, make inferences, and predict trends from data


  • Based on analysis of data and comparison to hypothesis

Theory??? Still not a fact, theories may change over time

opinion and fact
Opinion and Fact

Opinion: companies make advertisements are NOT fact; intended to persuade you

Fact: government studies and scientific research done by consumer magazines are usually more factual; no financial incentive to deceive you so more objective


Goggles to protect against liquid splashes and vapors

Add acid to water

NEVER smell or taste without permission


Periodic table: Locate

  • Metals – to the left of the stairstep
  • Nonmetals – to the right of the stairstep
  • Metalloids – along the stairstep
  • Group vertical column
  • Period – horizontal row
chemistry periodic trends
Chemistry – Periodic Trends

Number of valence electrons increases with increasing group number

Number of energy levels increases with increasing period number

Noble gases – Group 18; don’t form compounds; very stable; already have filled outer energy levels (octet)

chemistry classification of matter
Chemistry – Classification of Matter

Atom – smallest unit of a molecule or compound

Molecule – smallest unit of a substance

Element – made up of identical atoms; each element is identified by the # of protons

Compound –

  • Combination of two or more elements in an exact whole number ratio
  • Can only be separated chemically (break bonds)
classification of matter
Classification of Matter…

Mixture –

  • Combination of 2 or more compounds; no specific ratio
  • Can separate using physical means like sorting or filtering
  • Heterogeneous – unevenly mixed; can usually see the different substances
  • Homogeneous – evenly mixed; called a solution (can be a combination of any of the states of matter)
classification of matter1
Classification of Matter…

Physical change –

  • Same compound, just appears different; change of state, size, shape, mixture…
  • Done by physical means; force, average kinetic energy
  • Retains same chemical properties like boiling point, solubility, conductivity…
classification of matter2
Classification of Matter…

Chemical change –

  • Different substance due to chemical reaction; rusting, fading, burning, cooking, digestion, respiration, photosynthesis
  • Done by chemical reactions involving energy transformations
  • Need activation energy to get started; from sun, ATP, another chemical reaction, heat source…
  • Gains new chemical property “signature”
  • Evidence – color change, odor, formation of a gas or precipitate
classification of matter3
Classification of Matter…

Matter – particles; anything that has mass or takes up space

Mass – amount of matter an object has

Volume – amount of space an object takes up

Density – relates the object’s mass to its volume

  • Density effects many physical properties such as:
  • Viscosity – how easily a fluid flows
  • Buoyancy – how much upward force a fluid has or how much buoyant force is needed to make a solid float
types of chemical bonds
Types of Chemical Bonds
  • Metallic – 2 or more of the same metal
  • Ionic – 1 metal and 1 nonmetal; metal atom gives away 1 or more electrons, nonmetal takes them; forms charged ions that are then attracted to each other to make a compound
  • Covalent – 2 or more different nonmetals; share electrons to make compound
  • Diatomic – exactly 2 of the same nonmetal
types of chemical bonds1
Types of Chemical Bonds…

Polyatomic ion – 2 or more covalently bonded atoms that behave as a single unit to form ionic bonds with metals

naming ionic compounds
Naming Ionic Compounds
  • Ignore subscripts and coefficents
  • Write full name of first element or polyatomic ion in compound include roman numerals if needed
  • Write the first syllable of second element plus –ide OR the full name of polyatomic ion
naming covalent compounds
Naming Covalent Compounds
  • Use subscripts to determine prefix
  • Don’t use mono- if there is only one of the first element
  • Add –ide at the end
writing formulas
Writing Formulas
  • Write chemical symbol for first element or polyatomic ion in name
  • Write chemical symbol of second element or polyatomic ion
  • Write the oxidation number of each element or ion above the symbol (charge) and crisscross to use as subscripts
  • If they aren’t the lowest whole number ratio reduce
writing formulas1
Writing Formulas…
  • For covalent compounds just write the subscripts from the prefixes
balancing equations
Balancing Equations
  • Purpose – to follow the law of conservation of mass
  • Reactants – compound on the left side of the equation
  • Products – compounds on the right side of the equation
  • Compare the number of each element on the left side of the equation to the right side
  • Use coefficents to make equal
  • If an element show up in 2 or more compounds on the same side of the equation, balance it last! Usually oxygen or hydrogen
  • Check for simplest ratio
types of reactions
Types of Reactions

Based on chemical bonds

  • Synthesis: A + B  AB
  • Decomposition: AB A + B
  • Single displacement: A + CD  C + AD
  • Double displacement: AB + CD  CB + AD
  • Combustion: CxHy + O2  CO2 + H2O
types of reactions1
Types of Reactions…

Based on energy

  • Exothermic: need less energy to make reaction happen than it gives off when reaction is complete – Example: explosions, hot packs, glow sticks, burning
  • Endothermic: need more energy to make reaction happen than it gives off when reaction is complete – Example: cold packs
  • Solvent – substance that does the dissolving (water)
  • Solute – substance that gets dissolved (sugar)
  • “Like dissolves Like”
  • Polar solvent can dissolve ionic and polar solutes (ions); water is the universal solvent
  • Nonpolar solvent can only dissolve nonpolar solutes
  • Solubility
  • How MUCH of a substance will dissolve in a certain amount of solvent and at a certain temperature
  • Increase temperature, increase solubility for most substances except gases
  • Factors affecting the rate of solubility solids
  • Increase surface area (crushing)
  • Increase temperature (usually)
  • Agitation (stir)
  • Factors affecting rate of solubility gases
  • Decrease temperature
  • Increase pressure
  • Dissolving is a physical change
acids and bases
Acids and Bases
  • pH < 7 acid (lower the pH the stronger the acid)
  • pH = neutral
  • pH > 7 base (higher the pH the stronger the base)