Atoms and Elements Ch. 12

What is matter composed of? The Atom Smallest unit of an element that can still be identified as that element. A single atom is made up of smaller particles called subatomic particles.

What are atoms made of? Subatomic particles: Proton = positive electric charge Neutron = same mass as the proton but has no electric charge Electron = negative electric charge and is much smaller than a proton

Where are the subatomic particles found? Inside the nucleus Outside the nucleus Protons Neutrons Electrons Nucleus = the center of every atom

What makes elements different? All elements contain atoms and all atoms have the same subatomic particles What makes one element different from another?

Atomic Number The number of protons in an atom Identify the element Aluminum has 13 protons Gold has 79 protons Neon has 10 protons

Atoms are electrically neutral Each atom of a given element contains the same number of protons and electrons Aluminum = 13 protons + 13 electrons +13 + -13 = ???

Models of the Atom A long, long, long time ago… More than 2400 years ago Democritus, a Greek philosopher was the first person to suggest that everything was made of atoms

Democritus was not a popular guy…

1897: J.J. Thomson While investigating electricity, he discovered the electron He said it is really small and is negatively charged But everyone knew that objects didn’t have a charge….

Plum Pudding Model Plum Pudding Model = electrons are like raisins in plum pudding and the pudding cancels out the negative charge of the electrons

1911: Ernest Rutherford Gold Foil Experiment He found that Thomson was incorrect! Atoms are mostly empty space.

Gold Foil Experiment

1913: Niels Bohr Suggested electrons orbit the nucleus Today we know electrons don’t orbit…instead they are found in certain areas called electron clouds

Bohr’s Model of the Atom

Today’s Model of the Atom

Isotopes Not all atoms of the same element have the same mass What could change the mass of an atom but not change it’s identity? Isotope = atoms with the same number of protons but different numbers of neutrons

Elements Element = a substance that contains only one kind of atom Elements cannot be broken down into simpler substances Atomic number = the number of protons in an atom

Classifying Elements Metals Usually solids Conduct heat Conduct electricity Malleable = can be pounded into thin sheets Usually shiny

Classifying Elements Nonmetals Do not conduct heat Do not conduct electricity Dull Usually gases

Periodic Table Developed in 1869 A table that organizes the elements according to their atomic number Elements Song

Periodic Table

Periodic Table Each box on the periodic table contains information about each element: Name Atomic number Atomic mass Symbol

Periodic Table Name = Atomic Number = Atomic mass = Symbol =

Periodic Table Name = Atomic Number = Atomic mass = Symbol =

Periodic Table Name = Atomic Number = Atomic mass = Symbol =

Periodic Table Metals Nonmetals

Compounds Compound = a substance made of atoms of 2 or more elements that are chemically combined.

Table salt…a compound + =

Compounds Atoms in a compound stay together because they form bonds. Some atoms bond by sharing electrons. Some atoms bond by transferring electrons.

States of Matter Solids Definite shape Definite volume Atoms are tightly packed close together

States of Matter Liquids Definite volume No definite shape Takes the shape of its container Atoms are farther apart than they are in solids

States of Matter Gases No definite volume No definite shape Fills the entire volume of its container Atoms are the farthest apart

States of Matter Energy Solids = atoms have the least amount of energy Gases = atoms have the most amount of energy

Solids, liquids and gases

Changes of State Melting point The temperature at which a substance changes from a solid to a liquid

Changes of State Boiling point The temperature at which a substance changes from a liquid to a gas Also called evaporation

Changes of State Sublimation The temperature at which a solid changes directly to a gas

What causes a substance to change its state of matter? Adding or removing heat Heat is energy Adding or removing pressure

States of Matter Plasma A substance made of charged atoms, uncharged atoms, and electrons Happens when gases get very hot Rare on Earth Makes up 99% of the universe

Uses of Plasma Fluorescent bulbs Neon signs Computer chips Welding steel