Atomic Structure

Atomic Structure Defining the Atom

Eureka - Atoms

Meet the Elements Video clip

What is an Atom? The smallest part of an element that retains its identity in a chemical reaction.

Atomic History • http://www.youtube.com/watch?v=VQfOlMs4zFs&feature=related

HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which could not be divided and called these: ATOMA (greek for indivisible)

Historic Models of the Atom • Aristotle (384-322 BC) didn’t think there was a limit to the number of times matter could be divided. • He knew there were small particles. Air, Fire, Earth, Water

HISTORY OF THE ATOM John Dalton 1808 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

Dalton’s Atomic Theory • All elements are composed of atoms (which can’t be divided). • Atoms of the same element have the same mass and atoms of different elements have different masses. • Compounds contain atoms of more than one element. • In a compound, atoms of different elements always combine in the same way.

Dalton’s atom

Dalton’s Atomic Theory Most of Dalton’s statements are now known to be flawed. As we continue to study the atom, we will talk about discoveries that disproved Dalton’s statements. Scientists have revised the theory due to new discoveries!

HISTORY OF THE ATOM Joseph John Thomson 1898 found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

J.J. Thomson, 1897 • Discovered the electron, the subatomic particle with a negative charge • His experiments involved the use of a cathode ray tube Animation of Thomson’s model

JJ Thomson Question and explanation on youtube • http://www.youtube.com/watch?v=XU8nMKkzbT8

JJ Thomson Video clip • Start at 5:00 and go to about 7:00

HISTORY OF THE ATOM 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL

Developed the Plum Pudding model. (think of a chocolate chip cookie) Electrons evenly distributed throughout a positively charged material. Thomson’s Atomic Model

Plum Pudding Model Sphere of Positive charge e- e- e- e- e-

HISTORY OF THE ATOM Ernest Rutherford 1910 oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit

HISTORY OF THE ATOM gold foil helium nuclei helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

Ernest Rutherford, 1911 • Tested theory that electrons were evenly distributed throughout the atom within positively charged material • Performed the Gold-Foil Experiment

Rutherford animation

Another Rutherford Animation

Ernest Rutherford • If Thomson’s model was correct, most of the alpha particles should pass through with a little deflection

Rutherford’s Model • Proposed that atoms contain a nucleus, a small, dense, positively-charged sphere in the center of the atom. • Atom contains mostly empty space. • The nucleus is tiny compared with the atom as a whole.

Ernest Rutherford Rutherford’s model Thomson’s model

Rutherford’s model:Nuclear Atom e- e- e- + + + Rutherford did NOT know about neutrons!

HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

The Houston Astrodome occupies more than nine acres and seats 60,000 people. If the stadium were a model for an atom, a marble could represent its nucleus!

Development of the Atomic Theory Outline Activity HW- please work on page 1 of the Atom Worksheet and your Atomic Theory Outline/Foldable

Development of the Atomic Theory Timeline Activity – DAY 2 • Show me your timeline!!! • Let’s review those great scientists!!

Comparing Dalton, JJ Thomson, and Rutherford This is a one question quiz on youtube….

HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

Bohr’s Atom electrons in orbits nucleus

Summary • Dalton’s Theory- all matter is made up of atoms, which can’t be divided • Thomson’s Model- discovered atoms were made up of smaller particles (these smaller particles are charged) • Rutherford’s Theory- discovered the positively charged nucleus

Parts of an Atom • Atom = nucleus surrounded by one or more electrons • Atoms are neutral (no charge) • same number of protons as electrons. • Majority of the atom is empty space. • If nucleus were the size of a pencil eraser, the closest electron would be 100 yards away! • Subatomic Particles • Protons (+) • Neutrons (0) • Electrons (-) • Nucleus: Tightly packed Protons & Neutrons • Electrons Orbiting nucleus @ speed of light!!

HELIUM ATOM Shell proton N + - + N - neutron electron What do these particles consist of?

ATOMIC STRUCTURE Particle Charge Mass proton + charge 1 neutron No charge 1 electron - charge nil

Atomic Number • Atomic Number = # of Protons • Each Element in the Periodic Table has a different number of Protons, therefore each element has a different, unique, atomic number. When reading the Periodic table notice each element has a unique 1 or 2 letter symbol and “big” & “small” number listed

Eureka - Electrons

ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons

Can you read these?

Atomic Number and Mass Activity Contents of each box • Draw a box for your chosen element from your atom project and explain in detail what each of these are!! Atomic number Symbol Element name Atomic mass

Electrical Atomic Charge • Remember that Atoms are neutral (no charge) • So, the # of protons = # of electrons • If you know the Atomic #, you know the # of Protons and also the # of Electrons!! For example: Carbon has an atomic # of 6, it therefore has 6 Protons which has an electrical charge of +6, to make the atom neutral we need 6 negative charges found in the 6 electrons orbiting the nucleus.

Mass number (atomic mass) Atomic Mass = the total # of Protons & Neutrons ( we don’t worry about the mass of the electrons since they have almost no mass)

How many Neutrons are there? • Remember: • The Atomic # = the # of Protons • The Atomic mass = The # of both Protons & Neutrons. • Therefore, if you subtract the Atomic # (the number of Protons) from the Atomic mass (the number of both Protons & Neutrons) what is left over must be the number of Neutrons!! For Example w/ Carbon: Atomic Mass-Atomic # = # Neutrons Atomic Mass = 12, Atomic # 6 12 – 6 = 6 Therefore there are 6 neutrons present in the Carbon nucleus If you don’t believe me… just count for yourself.

Atoms with the same number of protons, but a different number of neutrons. “Same number of protons” means same atomic number, which means same element. “Different number of neutrons” means different mass numbers. What is an Isotope?

Isotopes • Can sometimes be represented with dashes and numbers that follow the element. • C-14 • Pu-246 • O-16 • O-17

Heavy Water • Video clip • Information about heavy water

Element Symbol Quiz • You need to know the element symbol for the following elements: • 1-20 • 24-30 • 35,47,50,53 • 79,80,82,86,88 • You will have a quiz on _____________ • I will give you the symbol or the name and you will have to give me the other…there will be NO WORD BANK!

Atomic Structure