APChem Ch.1

Atoms: smallest particle of an element that is indivisible

Element: a substance that can’t be broken down into a simpler substance

Compound: a substance made up of two or more elements bonded proportionally 

Law of definite proportions: a principle that states that a compound always contains the same proportion of elements 

Physical process: a transformation that doesn’t alter the chemical identities of a substance

• Ex. melting ice

Properties of matter

• Physical properties: properties that can be measured or observed without changing the substance into another substance

• Chemical properties: properties that can only be observed by reacting the substance with another substance

  • Ex. whether or not an element reacts with another and how quickly it reacts 

• Mass: the amount of matter in an object

• Density: the ratio of mass to volume

  • Formula: d=m/v

  • ImL=1cm^3

• Intensive properties: properties that are independent of the amount of substance

  • Ex. melting point, color, malleablility, and density 

• Extensive properties: properties that depend on the amount of a substance

  • Ex. Length, width, and mass

Chemical reactions: the conversion of one or more substances into another one or more substances

• Aka chemical change

Chemical bonds: the force that keeps two atoms or ion together in a molecule or compound

Most molecules are neutral but it they have a charge they are considered either monotomic (singular atom) or polyatomic (mant atoms)

Mixtures:  a combination of two or more pure elements with various physical and chemical properties who can be separated by physical processes

• Can either be homogeneous or heterogeneous

  • Homogeneous mixture: a mixture where the components are distributed evenly and the composition of uniform throughout

  • Hetergeneous mixture: a mixture where the components aren’t evenly distributed and there are different regions with different compositions

    • Immiscible liquids: a combination of liquid that do not combine or dissolve with eachother

Methods to separate mixtures

• Distillation: a process of evaporation and condensation to separate a mixture of substances with different volatilities 

  • Volatlities: a measure of how readily a substance evaporates 

    • The volatility is inversely proportional to the strength of the interactions between its particles 

      • As the strength of the interactions increases the probability decreases that the particles of the substance will have enough energy the break away in the liquid phase and become vapor

• Filtration: the process of separating solid particles from a liquid or gas by passing them through a filter or similar 

• Chromatography: It works by distributing the mixture between a stationary phase and a mobile phase, causing the components to separate based on their differing properties.

States of matter

• Solid: has definite volume and shape

  • Molecules are connected to eachother close together

• Liquid: has definite volume but not definite shape, the liquid takes the shape of the container

  • Molecules have the ability to move amongst eachother despite being close together

• Gas: has neither definite volume nor a definite shape, it expands to occupy the entire volume and shape of its container. It’s also highly compressible meaning it can fit into smaller volumes

  • Molecules are widely spread and the space between is just empty space making gases easily compressible

Methods of changing states of matter

• Sublimation: the transformation of solid directly to a gas

  • Endothermic (absorbs energy)

• Desposition: the transformation of gas directly to a solid

  • Exothermic (releases energy)

• Vaporization: the transformation of liquid to gas

• Condensation: the transformation of gas to liquid

• Melting/Fusion: the transformation of solid to liquid

• Solidification: the transformation of liquid to solid 

Energy: the capacity to do work

• Work: the exertion of force though a distance

  • Formula: w=fd 

• Potential energy: energy stored in an object due to its composition of position

• Kinetic energy: the energy of an object in motion due to its mass and speed (u)

  • Formula: 0.5mu^2

• The law of conservation of energy: energy can’t be created or destroyed but it can be converted

Some pure elements only exists diatomically

• Br, I, N, Cl, H, O, F

Structural formula: a representation of a molecule using lines and symbols to show chemical bonds

Ionic compound: a compound that contains positive and negative ions 

Molecular formula: a chemical formula that indicates how many atoms of each element are in one molecule of a pure substance

Empirical formula: a chemical formula which displays the subscipts with the smallest possible ratio of atoms or ions in the compound 

Absolute zero (0K): the zero point on the kelvin scale and theoretically the lowest temp possible 

Precision vs. Accuracy

• Precision: how repeatable a measurement is

• Accuracy: how close the value is to the true value

SigFigs: certain digits 

Conversion Factor: A fraction in which the numerator is equivalent to the demonimar but is expressed in different units, making the fraction equal 1

• Formula: Initial units x desired units/ inital units= desired units 

Mean/Arithmetic Mean: an average of all data points 

• Represented by a x̄

• Formula: Σi/n=x̄ (Σ= sum of all values)

Standard deviation (s) : a measure of the amount of variation in a value set

• Formula: s = √[ Σ (xi - x̄)² / n-1 ] 

  • X=value of data distribution

  • n= number of observations

  • x̄ =mean

Confidence interval: a range of values that has a specified probability of containing the true value of a measurement

Grubes test: a test that is used to detect a single outlier 

• Formula: Z=|xi-x̄|/s