History of the Atom Democritus Greek philosopher – 2000 years ago Model- all matter is made up of small indivisible particle Called atomos which means indivisible, can’t be cut

History of the Atom John Dalton English chemist – 1800’s Model- the atom is a sphere Foundation of modern chemistry

All elements are composed of atoms are indivisible, indestructible particles Atoms of the same element are exactly alike Atoms of different elements are different Compounds are formed by the joining of atoms of two or more elements

History of the Atom J.J. Thomson English scientist - 1897 Discovered a negative particle called the electron

History of the Atom J.J. Thomson Model- atom is a positively charged sphere with negatively charged electrons embedded throughout

History of the Atom Ernest Rutherford Model English physicist-1911 Atom is mostly empty space

Ernest Rutherford Model Contains a small positive dense core called the nucleus Electrons are scattered outside the nucleus

History of the Atom Niels Bohr Danish scientist-1913 Model- atom has a positive nucleus and the electrons move outside the nucleus in specific paths called energy levels (1-7)

History of the Atom Niels Bohr The further away the electron is from the nucleus the more energy it has

Niels Bohr Electrons can gain or lose energy Increase in energy when the electron raises or jumps to a higher energy level. Decrease in energy when the electron falls or drops to a lower energy level.

History of the Atom Erwin Schrodinger 1926 Based on wave mechanics

History of the Atom Erwin Schrodinger Model- electrons move very rapidly in regions of space around the nucleus This space is called the electron cloud

History of the Atom Erwin Schrodinger You don’t know the exact location of the electron just the most probable location.

Structure of the atom Nucleus Located in the center Positive charge Contains 99.9% of the mass of the atom

Structure of the atom Nucleus Protons Positively charged The number of protons in an atom identifies the type of atom

Structure of the atom Nucleus Protons Has a mass of 1 amu (atomic mass unit)

Structure of the atom Nucleus Neutrons Neutral charge Mass of 1 amu Helps keep the protons from repelling apart

Structure of the atom Atomic number Number of protons in the nucleus Located above the element symbol on the periodic table examples

Structure of the atom Isotope Same number of protons & electrons Atoms of the same element that has the same number of protons but a different number of neutrons Same number of protons & electrons Example: Hydrogen-1. Hydrogen-2, Hydrogen-3

Structure of the atom Isotope A sample of an element contains a mixture of all the isotopes of that element in nature

Structure of the atom Mass number Sum of the protons and neutrons of an atom Example: Carbon-14, carbon-12 Distinguishes one isotope from another

Structure of the atom Mass number Number of neutron = mass number – atomic number Examples: Uranium-235, Uranium-238

Structure of the atom Atomic mass Average mass of all the isotopes of that element as they occur in nature

Structure of the atom Atomic mass Round to find the mass number of the most common isotope of that element

Structure of the atom Electrons Negative charge Mass of 0.0006 amu Equal but opposite charge to that of a proton

Structure of the atom Electrons In a neutral, number of electrons equals the number of protons

Structure of the atom Electrons Can determine only the probability of the location of an electron that is in energy levels

Structure of the atom Electrons The amount of energy of an electron determines which energy level it will most likely be found

Structure of the atom Electrons Each energy level can hold a certain number of electrons, the maximum is…

Structure of the atom Electrons First energy level – 2 e- Second energy level –8 e- Third energy level – 18 e- Forth energy level – 32 e-

Structure of the atom Electrons The electron arrangement gives an element its chemical properties

Structure of the atom Electrons To be stable, an atom wants 8 electrons in its last energy level & it will bond to achieve this.

Electromagnetic force Forces within the atom Electromagnetic force Attraction or repulsion between charged particles

Forces within the atom Electromagnetic force Same charges repel – Ex – between two protons or two electrons

Forces within the atom Electromagnetic force Opposite charges attract – ex – between electron to proton

Electromagnetic force Forces within the atom Electromagnetic force Keeps the negative electrons orbiting around the positive nucleus

Forces within the atom Strong force Glues the protons together

Forces within the atom Strong force Only works at close distances

Forces within the atom Strong force Greatest force of the four

Forces within the atom Weak force Responsible for radioactive decay

Weak force Forces within the atom When neutrons change into a proton and an electron

Gravity Forces within the atom Force of attraction between objects of mass

Forces within the atom Gravity Weakest force of the four

Forces within the atom Gravity Can work over large distances

Nuclear Chemistry Reactions concerning the nucleus of the atom are considered nuclear chemistry.

Nuclear Chemistry Transmutation - change in the identity of a nucleus as a result of a change in the number of protons.

Nuclear Chemistry Remember: the number of protons determines the identity of the atom. Number of neutrons determine isotopes and number of electrons determine ions (or charge)

Nuclear Chemistry Radioactive Decay Unstable nuclei undergo radioactive decay to become more stable. Unstable nuclei have greater forces pushing it apart than holding it together.

Nuclear Chemistry Radioactive Decay: Applications Radioactive Dating Medicine: tracers, radiation therapy Agriculture: tracing fertilizer, shelf life Problems: Storage and disposal

Nuclear Chemistry nuclear fission a process in which a very heavy nucleus splits into more-stable nuclei of smaller masses

Nuclear Chemistry Nuclear Fission

Nuclear Chemistry Nuclear Fission chain reaction a reaction in which the material that starts the reaction is also one of the products and can start another reaction

Nuclear Chemistry Nuclear Fission Applications: Controlled: Power Plants and Nuclear Subs Uncontrolled: “The Bomb”

Nuclear Chemistry nuclear fusion the combining of light-mass nuclei to form a heavier, more stable nucleus

Nuclear Chemistry Nuclear Fusion

Nuclear Chemistry Nuclear Fusion Applications: The SUN! Maybe, someday, clean energy. Fusion requires high temperatures to work (like the sun). Scientist are trying to find a way to get a fusion reaction at lower temperatures.