Unit 2: Elements, Compounds and Mixtures

2.1 Energy  Energy- The capacity to do work or the ability to produce heat.  Work- force applied over a distance

The Forms of Energy  3 forms of energy: radiant, kinetic and potential.  Kinetic energy- this is the energy of motion.  aka- mechanical energy: moving machine parts.  aka- thermal energy caused by the motion of particles.  Potential energy- energy possessed (but not yet used) by an object due to its position/arrangement.  Aka- stored energy.  There are many types: gravitational, electrical and chemical.

Measuring Energy  SI unit for energy- joule (J).  Named after the English physicist, James Joule,  the amount of energy required to lift a medium apple 1 meter against the force of gravity.  How does this relate to the calorie?? Well:  1 cal = J  In chemistry we use joules not calories or Calories.

Law of Conservation of Energy (You must memorize or actually LEARN this law!) The total amount of energy in an isolated system remains constant. Energy cannot be created or destroyed! Only converted from one form to another.  Thanks to Joule’s work, this general law describes almost every situation possible…. Except one…. It does not apply/explain/justify what we see when we have a nuclear reaction.  Now we are talking about Nuclear energy… it’s special and doesn’t follow the rule.

2.2 Temperature  The necessity for detecting temperature has existed since the beginning of time. Initially, we only had the sense of touch (not the best). Then, Galileo Galilei invented the first “thermometer”.

The Fahrenheit & Celsius Temperature Scales  Gabriel Fahrenheit ( ) developed a scale which marked the freezing point of H 2 O as 32° and the boiling point as 212°.  Why?? Only he knows but this scale is not commonly used except for in the USA.

 Anders Celsius ( ) developed his scale and set the freezing point of H 2 O at 0° and marked the boiling point at 100°, thus creating a base 10 scale… much easier to use and that is why we use it in Chemistry.

Converting between the 2 scales  °F = 9/5 x °C + 32 or 1.8 x °C + 32  °C = 5/9 (°F – 32) or.55 (°F – 32)  Ex: convert 37.6 °C to °F convert 62.5 °F to °C

The Kelvin Temperature Scale  William Thomson, Lord Kelvin ( ) in the SI scale used to measure temperature. Here, 0 K is called absolute zero and represent the point at which the matter no longer has any kinetic energy. K = °C + 273

Try calculating these Temp. conversions  32K → ° C  K → ° C  26 ° C → K  ° C → K  25 °F → ° C  103°F → ° C  25 ° C → °F  10 ° C → °F

2.3 Matter  Matter:  Everything you see is made up of matter: YOU, your book, your desk, air.  Matter is anything that has mass and volume.  Light, sound and electricity are not matter and  do not have mass and do not occupy space

What exactly is matter and where did it come from? That is one of the great mysteries of life. But here is what we know so far…  There are 4 states of matter: solids, liquids, gases, and plasma. These states of matter are physically different.

Solid  Molecules do not move freely, they vibrate in place, giving solids a rigid structure.  They have ordered, fixed, and tightly packed arrangements due to chemical bonding and intramolecular interactions LEAST AMOUNT OF ENERGY

Liquids  Molecules are closer together and moves faster than solids.  Molecules are weakly attracted to one another moving less freely than gas. They move randomly and fill the container in which they are held.  The rate at which a liquid moves/flows is known as its viscosity.  The slower moving = more viscous. Ex: Glass.

Gases  molecules are in constant, random motion spreading out in all directions (diffusion).  They exert pressure. The pressure is made by individual gas molecules hitting the sides of the container.  As the temperature rises, the molecules begin to move faster → the pressure increases (the molecules hit the sides more often & with greater energy/force = increased pressure).

Plasma  Usually an ionized gas.  Does not have definite shape.  Conducts electricity well.  Effected by electric and magnetic fields. MOST AMOUNT OF ENERGY

Changes in State  Energy’s Role: required to move or change matter. Energy is transferred in all changes of state.  ENERGY REQUIRED - to melt or evaporate any substance.  Sublimation- physical change of a solid to gas - energy is required.

 Energy Released - during condensation or freezing. Gas → Liquid or Liquid → solid.  Changes of state:  solid → liquid → gas, does not change the composition or the mass.

Law of Conservation of MASS  Law of Conservation of MASS: MASS cannot be created or destroyed. Only transferred from one state to another.

Properties of Matter  Chemical Properties: how a substance reacts with other substances, chemically, to form new substances. *** composition will be changed***  Reactivity- the ability of a substance to react chemically with another substance. How much it will react depends on what they are reacting with and in what kind of environment the rxn is occurring.  Ex: rust (the ability of iron to react with oxygen), and combustion/flammability. Electronegativity, ionization potential, pH, heat of combustion, toxicity, stability…

 Physical Properties: characteristics of the substance which can be measured/observed without changing the composition of the substance.  Melting point - which a solid becomes a liquid.  Boiling point - which a liquid becomes a gas.  Density - the mass per unit volume.  Buoyancy - the force with which a more dense fluid pushes a less dense substance upward. * These properties help determine the use of the compound. *

 Chemical Changes: occurs when a substance changes composition to form a new substance.  Na 2 O + H 2 O → 2NaOH  Combustion:  CH 4 + 2O 2 → CO 2 + 2H 2 O

 Physical Changes: only the physical properties/form change. The substance may look different but the atoms of the substance are not changed.  Ex: changes of state- solid to liquid to gas. The substance looks different but the composition remains the same (H 2 O is still H 2 O). Grinding peanuts to make peanut butter. Pounding a gold nugget to make a ring

2.4 Elements & Compounds  What makes up matter?  Elements: a substance which cannot be broken down into simpler substances via chemical change.  Atoms - the smallest particle that has the properties of an element.

 Elements are represented by a 1 or 2 letter symbol.  For example C is carbon, O is oxygen, Fe is iron, Al is aluminum and Na is sodium.  There are more that 110 elements we know of and all have distinct properties and behaviors

 Compounds: When 2 or more elements combine chemically they form a compound (a substance made of atoms of more than one element bound together).  Every compound is unique and different from the elements it contains.  EX: Sugar C 6 H 12 O 6.  Compounds have set ratios.  EX: Water will always have 2 H atoms to every 1 O atom.

 Molecules: when elements combine to form compounds the smallest unit that exhibits all the properties of the compound is a molecule. Most molecules are made of atoms from different elements (H 2 O) but some are made of the same element.  EX: Ne, O 2, H 2, Cl 2, P 4, S 8.  A pure substance is matter with a fixed composition and definite properties.  EX: isopropanol.  Pure substances blend together to make mixtures. C3H8OC3H8O

2.5 Mixtures  Mixture- a combination of more than one pure substance. Think of grape juice… it is a mixture. It is made of many compounds that can be separated: H 2 O, sugars, acids and other compounds. It also doesn’t have a fixed composition: the amounts of H 2 O, sugar, etc. change every time you make the juice.  *** Mixtures will share some of the properties of the pure substances that make it.  Ex: grape juice shares the wetness of H 2 O and the sweetness of the sugar.***

Mixtures are classified by how they mix.  Heterogeneous mixtures: are mixtures that do not uniformly mix together.  Ex: flour and H 2 O.  Homogeneous mixtures: mix uniformly through out.  Ex: H 2 O and NaCl (table salt) or C 6 H 12 O 6.

 Miscible: liquids which are able to dissolve into each other.  Ex: isopropanol and H 2 O.  Immiscible: 2 liquids which do not mix/dissolve into one another.  Ex: Oil and H 2 O.  Gases can mix with liquids; think of soda/pop.