ATOMS! Mr. Coffey MODELS! A MODEL: is a representation that shows the construction or appearance of something. As our technology has evolved our theories and models have also evolved. Models of the atom have changed through the years as we have discovered new things.

Some History Meet DEMOCRITUS (about 2400 years ago) Remember how questions are important? Well Democritus asked: Can I cut something in half FOREVER? He decided NO; with the help of his students they were the first to name the smallest piece: ATOM , which means CANT DIVIDE.

How does an atom behave? Democritus and his students didnt know what atoms looked like so long ago. They thought atoms were very small, hard particles and were made out of the same material but had different shapes and sizes. They also thought atoms were infinite in number and that they were always moving and could be joined together. Then there was DALTON 1800s

He said the atom was a CANNONBALL that it cannot be divided into anything smaller. Some of his theories have been proven wrong, or evolved into our current theories. His model is called the Cannonball Model. Daltons Atomic Theory of Matter All elements are composed of atoms. Atoms cant be divided or destroyed. Atoms of the same element are exactly alike. Atoms of different elements are different from

each other. The atoms of 2 or more elements can join together to form types of matter called compounds. J.J. Thomsons Model The first scientist to suggest that an atom contains smaller particles was J.J. Thomson of England in 1897. Thomson discovered electrons using a cathode ray tube while studying atoms. Because atoms are neutral, Thomson reasoned that there must also be positively charged particles inside

the atom. J.J. Thomsons Model Thomson hypothesized that an atom was made up of positively charged material with negatively charged particles scattered evenly throughout the atom. His model was called the Plum Pudding Model.

Electrons Plum Pudding electrons are scattered like raisins in pudding. Rutherfords Model In 1911 a British scientist named Ernest Rutherford performed an experiment to test Thomsons atomic model. He discovered that an atom is mostly empty space.

He said that the center of the atom is a small, dense nucleus that is positively charged. Rutherfords Model Rutherford said the negatively charged particles were attracted to the positively charged particles found in the nucleus. He said this attraction holds the negatively charged particles in the atom. He didnt really

address electrons. Bohrs Model This is what is on Jimmys shirt! 2 main pieces of an atom: 1. a NUCLEUS containing positively charged protons and 2. The ELECTRONS that orbit around the nucleus much like planets orbiting around the sun. He called these orbits electron

shells. The Bohr Model What is true today: The nucleus ( the center of the atom)is composed of 2 things: PROTONS (positively charged particles) NEUTRONS (neutral-charged particles) The electrons do not move in orbits like Bohr said. Electrons are in a cloud they are in orbitals,

or regions of probable electron location. They DO move around the nucleus in different patterns. Wave-Mechanical Model Electrons are moving so fast that they look like a cloud. Orbitals are regions of most likely electron location. All Models!

Daltons model (Cannonball) JJ Thomsons model (Plum pudding) Rutherfords model Orbitals Bohrs model (planetary)

Current Orbital model Some things to remember: Atoms are the building blocks of EVERYTHING! Atoms are made up protons, electrons, and neutrons. Components of an Atom a. Atoms are the building blocks of EVERYTHING!

b. Atoms are made up of subatomic particles Sub means smaller or less than. Atomic means atom. c. So subatomic particles are the smaller particles (parts) that make up an atom. d. The 3 subatomic particles are: protons electrons neutrons Meet the ATOM! Subatomic

Particle Protons Neutrons Electrons Location in the Atom Center (in the nucleus) Center (in the nucleus) Around the nucleus in

clouds or orbitals Charge Weight + (Positive) 1 amu* Neutral (no charge)

- (Negative) 1 amu Almost none! It rounds to 0 amu *Amu means Atomic Mass Unit AMU a. AMU= Atomic Mass Unit b. This is the unit of measure scientists use to measure the mass of an atom.

c. 1 amu = mass of 1 proton or 1 neutron d. The mass of an electron = 1/1836 amu PROTONS ELECTRONS POSITIVE charges NEGATIVE charges FLY around the Found in the

CENTER of the nucleus in atom - aka nucleus orbitals or energy levels! HEAVY! (1amu) LIGHT! So light in fact, that they dont factor in to the mass of an atom! Back to the atomwhy it works Forces hold the atom together. Remember that opposite

charges attract and like repel! The electrons are moving so fast that they stay in orbit around the positive nucleus, the same way we stay in orbit around the sun. Remember elements? An element, remember, is a substance that cannot be chemically broken down into simpler things! Elements are made up of ATOMS! There are many different elements There are about 118 known today. Theyre organized and arranged on the Periodic

Table! # of Protons in an Atom Every element on the periodic table has a different number of protons, neutrons and electrons. Atomic Number = Number of Protons Number of Protons = Number of Electrons Mass of an Atom The Mass is the TOP #. Round to the nearest whole number. In this example, the mass of carbon is 12.

# of Neutrons in an Atom The number of neutrons is equal to the mass minus the number of protons. Top # Bottom # = # of neutrons 12 mass 6 protons 6 neutrons Some examples! Mass

Mass Mass Mass Mass 11 12 14

16 19 # of protons # of protons # of protons # of protons

# of protons 5 6 7 8 9 # of neutrons

# of neutrons # of neutrons # of neutrons # of neutrons 6 6

7 8 10 A harder example Mass: 197 # Protons: -79 # Neutrons: 118 #Protons = #Electrons 79 Protons = 79 Electrons

Models of Elements According to the Periodic Table, Carbon has a mass of 12 and has 6 protons. 12 6 = 6 neutrons. This tells you where the electrons go in shells. Here, there are 2 shells. 2 electrons go in the first shell and 4 go in the second shell.

An atom of oxygen 8p 8n This tells you 2 shells: 1st shell has 2 electrons 2nd shell has 6 electrons One more! 11 p

12 n This tells you 3 shells: 1st shell has 2 electrons 2nd shell has 8 electrons 3rd shell has 1 electron Ions a. If an atom gains or loses electrons it has a charge. The charge could be positive (if the atom loses electrons) The charge could be negative (if it gains electrons).

b. An atom is still the same element if it gains or loses electrons, it just now has a charge. c. We call an atom with a charge an ion. Isotopes a. Isotopes-atoms of the same element that have the same number of protons as the other atoms of the element but a different number of neutrons. b. Just like an ion, an isotope is still the same element. It is just a little different from every other atom of the same element. c. For example-A carbon atom can have 12 neutrons or 14

neutrons. It is still carbon. It just has a slightly different mass. i. Think of a pillow- some have more stuffing than others so their mass may be different but they are still all pillows.

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