Kinetic Molecular Theory

A Summary of Ideas All matter is made up of very small particles that are constantly moving The more energy particles have, the faster they can move and the farther apart they can get. Matter expands when its temperature is raised and contracts when its temperature is lowered. If enough energy is added to or removed from matter, the matter changes from one state to another.

What is matter? Anything that has mass and volume. Mass = the quantity of matter that a substance or object contains or how heavy something is Volume = the amount of space taken up by a substance or object

Recall: 3 states/phases of matter Solid = definite shape and volume Liquid = definite volume but its shape is determined by its surroundings Gas = volume and shape determined by its surroundings

The Particle Model All matter is made up of very small particles (too small to see with the naked eye) There are spaces between the particles, the amount of space depends on the state of matter. Particles that make up matter are always moving Particles are attracted to one another, the strength of the attraction depends on the type of particle.

Kinetic Molecular Theory Kinetic energy = the energy of motion All particles have kinetic energy KMT explains what happens to matter when the kinetic energy of particles changes.

Kinetic Molecular Theory All matter is made of atoms and molecules There is empty space between these particles These particles are constantly moving (colliding with each other and walls of their container) Energy makes particles move, the more energy they have the faster they can move and the further apart they can get “Energy” “Particle”

Particles of a solid = tightly packed together - Can’t move around freely, can only vibrate Particles of a liquid = farther apart and move by sliding past each other Particles of a gas are very far apart and move around quickly

Thermal Expansion Adding energy to a material increases the kinetic energy of the particles Example: Adding heat As energy is added the particles move around faster and farther; creates more space between particles The material that is made up of the particles expands/increases in volume

Thermal Contraction When temperature/energy is removed from a substance the movement of particles slows down, particles take up less space The matter contracts/decreases in volume

Different materials expand or contract with changing temperature at their own particular rate (different matter different melting points!) Ex: aluminum will change 3x more than glass for the same change in temperature

What is the difference between heat and temperature? Thermal energy = total amount of energy of a substance If two substances with different thermal energies come in contact, energy will flow from high concentration to low concentration Heat = energy transferred from one material to another because of a difference in temperature/change in state Temperature = the average kinetic energy of a substance’s particles

Changes of State If temperature is continually raised: Particles move farther and farther apart: solid  liquid  gas (evaporation) If temperature is continually lowered: Particles move closer together: gas  liquid (condensation)  solidification Sublimation = solid  gas Deposition = gas  solid (ex. frost on windows)

Atomic Theory Dalton’s atomic theory was the first attempt to describe all matter in terms of atoms and their properties Theory is based on the law of conservation of mass and the law of constant composition

Matter is not created or destroyed in a closed system (put a lid on it Matter is not created or destroyed in a closed system (put a lid on it!) If we have a chemical reaction, the amount of each element must be the same in the starting materials (reactants) and the products

Atomic Theory: #1) All matter is made of atoms, which are indivisible Even if we can’t see atoms with our naked eye, properties of matter such as colour, phase, and even smell come from interactions on an atomic level Dalton imagined atoms as “solid, massy, hard, impenetrable, moveable particles” Atoms are not solid spheres Atoms are made up of protons, neutrons and electrons

Atomic Theory: #2) All atoms of a given element are identical in mass and properties

Atoms of the same element have different masses because the number of neutrons can vary for different isotopes of a given element They will have the same number of protons because that is what identifies them as being a particular element

Atomic Theory: #3) Compounds are combinations of two or more different types of atoms Example: Table salt = Na (sodium) + Cl (chlorine) 2 separate elements with unique physical and chemical properties Na = highly reactive metal Cl = toxic gas When they react, the atoms combine in a 1:1 ratio to form white crystals of NaCl Since atoms are indivisible, they will always combine in simple whole number ratios (ie. You can’t have half an atom)

Atomic Theory: #4) A chemical reaction is a rearrangement of atoms Chemical reactions don’t destroy or create atoms, they rearrange them Ex: Salt  both sodium and chlorine atoms still exist but they have rearranged to form a new compound

Atoms Are the basic units of matter They are the defining structure of elements The term “atom” comes from the Greek word for indivisible Atoms are made up of protons, neutrons and electrons These are composed of even smaller particles (quarks and leptons)

Building an element from the ground up After the “Big Bang” 13.7 billion years ago, the hot, dense and new universe cooled just enough so that conditions became suitable for quarks to form Think of a quark as the beginning building block to create the nucleus of an element. Quarks

380, 000 years later the universe cooled enough to slow down the electrons so that the nuclei could capture them to form the first atoms Imagine how fast particles would be moving around with the extreme thermal energy from the Big Bang?! The earliest atoms were primarily hydrogen and helium, which are still the most abundant elements in the universe. Gravity eventually caused clouds of gas to coalesce and form stars, and heavier atoms are created within the stars and sent throughout the universe when the star explodes (called a supernova)

So what composes an atom? A quark is a particle Quark particles come together to form “composite particles” called hadrons (protons and neutrons) Element nuclei are made up of a combination of protons and neutrons Electrons are a type of “lepton”

Protons and Neutrons Heavier than electrons Reside in the nucleus at the center of the atom Have approximately the same mass The number of protons and neutrons is usually the same in an atom Adding a proton to an atom makes a new element Adding a neutron makes an isotope, or a heavier version, of that atom

Electrons Extremely lightweight Exist in a cloud orbiting the nucleus One proton weighs more than 1800 electrons Exist in a cloud orbiting the nucleus Electron cloud has a radius 10, 000 times greater than the nucleus