“Atomic Structure”

“Atomic Structure” Chemistry- power point adapted from Charles Page High School Stephen L. Cotton /R Wolfendale/ Derek Stacy

Defining the Atom • OBJECTIVES: • Describe the structure of an atom • Outline development of atomic models • Atoms/ions-the difference • Using chemical formulas to identify ionic compounds • Distinguish between chemical and nuclear reactions • Compare protons, neutrons and electrons • Describe how Alpha and Beta particles and Gamma radiation are released from unstable atoms

The Atom- SW pg69 + P 4+ • Everything is made of atoms-WOOD, GLASS, SKIN • They are so small you cannot see them even with a microscope • There are 118 known types of atoms, 91 that are natural on earth, the other 27 made in the lab • Atoms are listed smallest to largest on the periodic table • Each square has the atom, its chemical name and symbol • (students to receive periodic table to stick in book and blank one to label later

Elements Year 9 Science Pure substances can be further classified as elements and compounds. Elements are the building blocks of all other substances. Elements consist of atoms of the same type and are represented separately on the periodic table. Elements cannot be broken down further by chemical processes. E.g. calcium, oxygen, zinc, chlorine, carbon, iron, etc

Common elements Oxygen-O2 Phosphorus-P4 Made of 60 Carbon atoms in the shape of a soccer ball Buckyball- carbon 60

Molecules Year 9 Science Elements are made up of characteristic atoms and they can join together to form discrete groups of atoms called molecules. It is often in a grid or crystal lattice like structure Two hydrogen atoms can join with an oxygen atom to form a water molecule. H2O

Crystal Lattice Silicon and oxygen atoms form crystal lattices to make beach sand! Depending on how big the sand grain-determines how many atoms

Compounds Year 9 Science Compounds are pure substances that can be broken down further by chemical reactions. E.g. water, sugar, polythene, propane, sodium chloride, etc, Water (H2O) can be broken down into the elements hydrogen and oxygen by the process of electrolysis. water → hydrogen + oxygen electricity

Compounds Year 9 Science Sodium chloride (NaCl) a compound, called a crystal lattice, can be broken down into the elements sodium and chlorine, also by electrolysis. sodium chloride → sodium + chlorine electricity

Compounds Year 9 Science Compounds can also be synthesised (man made) by reacting elements together. A compound is defined as having more than one type of atom. When hydrogen is burned in oxygen water is produced. hydrogen + oxygen → water

Compounds Year 9 Science Compounds have very different properties to those of the elements that make them up. Sodium (Na) : very active metal Chlorine (Cl2): a poisonous gas Sodium chloride (NaCl): our bodies need for cellular processes. + → sodium chlorine sodium chloride

Inside the Atom

Atoms Year 9 Science Protons and neutrons exist in the central part of the atom called the nucleus. Electrons orbit the nucleus in energy levels called shells. Electrons cannot exist in the nucleus. They are much smaller and move very fast This speed of the electrons forms an electron cloud

Subatomic Particles

Atoms Year 9 Science The number of protons in the nucleus is characteristic of the element and is called the atomic number. All hydrogen atoms have 1 proton. … All uranium atoms have 92 protons. Etc.

Atomic Number The number of protons in the nucleus of an atom= Atomic Number –the number you see on the periodic table above the symbol/name Number of protons and neutrons in the atom’s nucleus is the MASS number

Isotopes • Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912 • Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. • Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.

Isotopes Sometimes atoms of the same element have different numbers of neutrons from one another- e.g. Helium has generally 2 protons/2 neutrons Mass number = 4 in this case However there is a HELIUM 3 2 PROTONS AND 1 NEUTRON –Mass= 3 When the atomic number is the same but mass number different for the same element- it is called an Isotope

Isotopes cont: Almost all elements have two isotopes Some have many more Most common isotope is Hydrogen 1 = 1 proton in nucleus and no neutron Makes up 99.98 % of the hydrogen on earth-called protium Hydrogen 2 is deuterium, and Hydrogen 3 = tritium It is the isotopes of hydrogen that are used in nuclear power plants to generate power more efficiently

Isotopesare atoms of the same element having different masses, due to varying numbers of neutrons.

A look back then!Defining the Atom • The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) • He believed that atoms were indivisibleand indestructible • His ideas did agree with later scientific theory, but did not explain chemical behaviour, and was not based on the scientific method – but just philosophy

Thomson’s Atomic Model J. J. Thomson Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Dalton’s Atomic Theory (experiment based!) All elements are composed of tiny indivisible particles called atoms Atoms of the same element are identical. Atoms of any one element are different from those of any other element. John Dalton (1766 – 1844) Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.

Sizing up the Atom • Elements are able to be subdivided into smaller and smaller particles – these are the atoms, and they still have properties of that element • If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long • Despite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) microscopes

Section 4.2Structure of the Nuclear Atom • One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles: • Electrons, protons, and neutrons are examples of these fundamental particles • There are many other types of particles, but we will study these three

Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron

Modern Cathode Ray Tubes Television Computer Monitor • Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Mass of the Electron Mass of the electron is 9.11 x 10-28 g The oil drop apparatus 1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge

Conclusions from the Study of the Electron: Number of electrons = number of protons: This means atoms have a neutral charge because = +’ve charges = - ‘ve charges Electrons have so little mass = they are so small that atoms contain electron clouds (all the electrons flying round the nucleus) these can be huge -1000 X wider than the nucleus Most of an atom is therefore empty space

Conclusions from the Study of the Electron: • In New Zealand a scientist Earnest Rutherford discovered that the nucleus took up such a small space inside the atom • He fired a beam of helium nuclei)alpha particles, into a piece of gold foil – most passed through to his surprise! Some deflected back • Up till now most scientist thought atoms were quite solid

Ernest Rutherford’sGold Foil Experiment - 1911 • Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil • Particles that hit on the detecting screen (film) are recorded

Electrons….. The electrons are attracted to the nucleus by the protons in the nucleus because of their opposite charges Why don’t they “fall into the nucleus”?....they are trapped in electron shells These are a little like layers on an onion Many of the shells in an atom are empty as obviously many atoms do not have many electrons Electrons have set numbers than can be held in each shell…i.e the first shell and smallest holds two The next can hold 8, the third is 18, 4th is 32 and so on…works on a formula 2n squared The number of electrons in each shell is the ELECTRON CONFIGURATION I.E Sodium is 2:8:1 as it has 11 electrons…..

Structure of the Nuclear Atom • Practical pg 11 (P) Experimenting like Rutherford • Describe the structure of atoms, according to the Rutherford atomic model.

Some revision- before Ions! Complete Symbols Element, the mass number and the atomic number. Mass number X Superscript → Atomic number Subscript →

Symbols • Find each of these: • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35

Symbols • If an element has an atomic number of 34 and a mass number of 78, what is the: • number of protons • number of neutrons • number of electrons • complete symbol

Symbols • If an element has 91 protons and 140 neutrons what is the • Atomic number • Mass number • number of electrons • complete symbol

Symbols • If an element has 78 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • complete symbol

“Atomic Structure”