What is chemistry?

• Chemistry: the study of matter and the changes that matter undergoes

• Matter: anything that has mass and takes up space

  • Living and nonliving things are all matter

• Areas of chemistry?

  • Organic chemistry

    • Studies all carbon based compounds

  • Inorganic chemistry

    • Studies all chemicals that do not contain carbon

  • Biochemistry

    • Studies the processes that take place in organisms

  • Analytical chemistry

    • Focuses on the composition of matter

  • Physical chemistry

    • Deals with mechanism, rate, and energy transfer that occurs when matter undergoes a change

• Accuracy vs Precision

  • Accuracy: having responses close to the correct/accepted value

  • Precision: having responses close together but not near the correct/accepted value

• Pure vs Applied chemistry

  • Pure chemistry: the pursuit of chemistry for its own sake

    • No immediate practical use of chemistry

  • Applied chemistry: research directed to a practical goal

Working with measurement

• 7 SI base units

• Conversions

  • 38,000 kg → x1000 → 38,000,000 g

  • 0.02km → x100,000 → 2000 cm

  • 4.3 ms → /1000 → 0.0043 s

• Scientific Notation

  • 41,000 → 4.1 x 10^4

  • 0.0029 → 2.9 x 10^-3

  • 123,000,000 → 1.23 x 10^87y

Physical and Chemical Properties

• Matter: anything that has mass and takes up space

• Substance: matter that has a uniform and unchanging composition

  • Ex: table salt

• Physical properties: a characteristic that can be observed or measured without changing the sample’s composition

  • Ex: density, color, odor, taste, hardness, melting point, boiling point, texture, conductivity, luster, length, volume, weight, magnetism, tensile strength, malleability

• Extensive properties: dependent upon the amount of substance present

  • Length, volume, mass

• Intensive properties: independent of the amount of substance present

• Chemical properties: the ability of a substance to combine with or change into one or more substances

  • Ex: rusting, combustibility, reactivity, oxidization, flammability

Physical and Chemical changes

• Physical changes: when a substance doesn’t change its composition, just its appearance

  • Ex: crumpling aluminum/paper, ice melting, water freezing, breaking something, boiling, condensation

• Chemical changes: a process that involves one or more substances changing into new substances

  • Ex: rusting, baking soda + vinegar, baking, burning wood, photosynthesis, explosions, rotting, corrosion, tarnish, ferment, oxidize

  • The new substances formed have different compositions than the original substances

• Law of Conservation of Mass

  • By carefully measuring mass before and after many chemical reactions, it was observed that the total mass involved remained constant

  • M reactants = M products

Mixtures

• mixture: a combination of two or more pure substances

• Substances tend to mix naturally- it it difficult to keep them pure

• Heterogeneous vs Homogeneous mixtures

  • Heterogeneous: individual substances remain separate, not mixed smoothly

    • Sand and water

    • Iron and sand

    • Trail mix

    • Blood

  • Homogeneous: has a constant composition throughout, fully mixed

    • Also known as a solution

    • Types of solution

      • Gas-gas

        • air

      • Gas-liquid 

        • Carbonated drinks

      • Liquid-gas 

        • Water vapor in the air

      • Liquid-liquid 

        • Vinegar and water

      • Solid-liquid 

        • Powdered drink mix

      • Solid-solid 

        • Steel

    • Solid-solid

      • Also known as alloy:

        • Alloy: a homogeneous mixture of metals, or a mixture of a metal and a nonmetal

Methods of separating mixtures

• Filtration

  • Used to separate some mixtures of solids and fluids

• Sedimentation

  • The deposition of sediments

  • Takes place when particles in suspension settle at the bottom of the beaker

• Decantation

  • A process for the separation of mixtures of immiscible liquids or of a liquid and a solid mixture such as a suspension

• Distillation

  • The process of separating components of a mixture based on different boiling points

  • Simple distillation: used when the ingredients of liquid mixture have changes of the boiling point close to 50 degrees

  • Fractional distillation: used for mixtures that have closer boiling points

• Crystallization

  • A technique used for purification of substances

  • Used to separate solids from a solution

• Chromatography

  • A technique that separated a mixture based on the tendency of each to travel or be drawn across the surface of another material

• Sublimation

  • The technique where a substance makes a transition from the solid to the gas state directly

• Extraction

  • The first step to separate the desired natural products from the raw materials

• Magnetic Separation

  • The process of separating components of mixtures by using a magnet to attract magnetic substances

Elements and Compounds

• Element: a pure substance that cannot be separated into simpler substances by physical or chemical means

• Periodic table: organizes the elements into a  grid of horizontal rows called periods and vertical columns called groups or families

  • Each element has a unique name, symbol, atomic number, and atomic mass on the periodic table

  • Dmitri Mendeleev came up with the rows and column system

  • Elements in the same group have similar properties

• Compound: a combination of two or more different elements that are a combined chemically

  • Ex: water, table salt, table sugar, aspirin, baking soda, carbon dioxide, vinegar

  • Currently there are around 10 million compounds discovered, with 100,000 made/discovered each year

  • The chemical symbols on the periodic table make it easy to write the formulas for chemical compounds

    • H2O, NaCl

  • Can be broken down into simpler substances by chemical means

Law of Definite Proportions

• Regardless of the amount, a compounds is always composed of the same elements in the same proportions

• Mass of compounds = sum of masses of the elements that make up the compounds

• Percent by mass: the ratio of the mass of each element to the total mass of the compound

• % = mass of elements/mass of compounds x 100

• Examples: 

  • Calculate the percent by mass of N in NH3

    • m(N) = 14.01 g/mol

    • m(H) = 1.01 g/mol

    • % N = m(N)/m(NH3) x 100

    • % N = 14.01/17.04) x 100 = 82.22%

Law of Multiple Proportions

• When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small numbers

• Ratios compare the relative amounts of any items or substances

• Different compounds exist of the same elements in different combinations

History and Structure of the Atom

• Origin of the atom

  • Democritus- ancient Greek Philosopher

  • Proposed the existence of atoms

  • Everything is made of atoms and they can’t be destroyed 

  • Atomus: (Greek) undivided

• John Dalton

  • First to provide scientific evidence that the atom exists

  • Cannonball model: atoms are indestructible spheres that combine to form compounds

    • Atoms of the same element are identical

    • Atoms can combine in more than one ratio (law of multiple proportions)

    • During a chemical reaction, atoms can rearrange

• JJ Thompson

  • Proposed the existence of the first subatomic particle (the electron)

  • Plum pudding model: atoms have an overall positive charge with regions of randomly-dispersed negative charge

• Ernest Rutherford

  • Discovered the nucleus using the gold foil experiment

  • Nuclear model: the atom has a nucleus and the electrons move around it

• Niels Bohr

  • Studied emission light spectrums of different elements

  • Planetary model: electrons orbit the nucleus like planets orbit the sun

• Heisenberg

  • Electron cloud model: electrons behave as waves and occupy regions of space surrounding the nucleus called orbitals