Chapter 11 Introduction to Atoms

An atom is the smallest particle into which an element can be divided and still be the same substance. See timeline handout for the development of the model of the atom. Identify atom models of Dalton, Thomson, Rutherford, Bohr, and the Modern Model.

Structure of the atom nucleus energy level

What do I need to know? Know the scientist their contribution to the developing model of an atom (their experiment) their atom model!

Dalton’s Atomic Theory Today, we are going to look at the development of the atomic theory. We are going to define Dalton’s atomic model.

Which is not part of Daltons Theory? Atoms cannot be divided, created, or destroyed. All atoms of an element are identical. Chemical Reactions destroy matter. Atoms combine in specific ratios.

Which is not part of Daltons Theory? Atoms cannot be divided, created, or destroyed. All atoms of an element are identical. Chemical Reactions destroy matter. Atoms combine in specific ratios. Chemical Reaction Rearrange atoms.

Thomson’s Atomic Model Then we are are going to look at Thomson’s modifications, or Thomson’s atomic model.

Thomson’s Atomic Model: A sphere with an evenly distributed positive charge with negative electrons mixed in - - - - - Thomson’s Atomic Model said that an atom is a sphere with an evenly distributed positive charge with negative electrons mixed in - -

Cathode Ray Tube Thomson began experimenting on a cathode ray tube to see if rays had charges.

Cathode Ray Tube In his experiment, Thomson shot cathode rays through a tube and saw the wire bend towards the positive plate.

Why did Thomson’s experiment lead him to believe cathodes were negatively charged? The wire bent towards the positive

Thomson’s Atomic Model: A sphere with an evenly distributed positive charge with negative electrons mixed in - - - - - - As a reminder, Thomson’s Atomic Model said that an atom is a sphere with an evenly distributed positive charge with negative electrons mixed in. Just like a plum pudding. -

What charge does the red section have? Positive.

Why are there both positive and negative charges? The overall net charge is neutral.

Rutherford Atomic Model Then we will define Rutherford’s Atomic Model.

Rutherford’s Atomic Model: atoms consist of a positive center surrounded by electrons in negative space Positive Center Atoms have a positive center surrounded by electrons in negative space

Gold Foil Experiment Here Rutherford shown alpha particles at a piece of gold foil and expected the particles to travel straight through

Reflection Instead the light was sometimes reflected.

Dense Space= Reflected by Foil This meant the alpha particle was hitting a dense space when it was reflected.

Empty Space= Through Foil This meant the alpha particle was hitting empty space, when it traveled through.

Positive central nucleus Rutherford concluded there was a positive central core, or the nucleus

Electrons in empty space And also that that electrons are in the negative space.

Rutherford’s Atomic Model: atoms consist of a positive center surrounded by electrons in negative space Positive Center So, he knew that atoms have a positive center surrounded by electrons in negative space

Where is the positive charge located? The nucleus

What experiment did Rutherford use? The Gold Foil Experiment.

Why is the atom mostly empty space? Most of the particles went through the foil.

Bohr’s Atomic Model Bohr’s Atomic Model will also be discussed.

Bohr’s Atomic Model: electrons move in orbitals and, when they change orbitals, they gain energy

What did he observe to discover this model?

Modern Atomic Model And finally we will address the modern atomic model.

Modern Atomic Model

Modern Atomic Model: orbitals are clouds and shows where electrons are most likely to be The modern model is similar to Bohrs model except it looks at orbitals as clouds. Instead it shows the area where the electron is most likely to be.

Which model defines the characteristics of an atom? Dalton

Which model has a positive sphere with negative charges embedded? Plum Pudding

Which scientist introduced orbitals? Rutherford

How is Bohr’s Model different from Rutherford’s? Bohr included oribtals.

What is the key characteristic of modern atomic theory? Electron cloud

Structure of the atom The atom contains a nucleus surrounded by one or more electrons The nucleus contains protons and neutrons. Draw an atom here (Page 320)

Structure of the atom nucleus energy level

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral Electron Negative (-) Outside nucleus 1/2000 amu

Particle Charge Location Mass Proton

Particle Charge Location Mass Proton Positive (+)

Particle Charge Location Mass Proton Positive (+) Inside nucleus

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral Electron

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral Electron Negative (-)

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral Electron Negative (-) Outside nucleus

Particle Charge Location Mass Proton Positive (+) Inside nucleus 1 amu Neutron Neutral Electron Negative (-) Outside nucleus 1/2000 amu

Terms to copy in notes: atomic number – the number of protons in the nucleus of an atom. (*The number of protons identifies an element!) atomic mass – the average mass of one atom of an element. atomic mass unit (amu) – a measurement of the mass of one proton or one neutron.

Know the Following Elements! The first 20 elements and symbols, plus 7 others, must be properly identified together. iron copper silver gold mercury tin lead The symbols must be written in correct form. Spelling counts!

Chemical Symbols Hydrogen symbol is H Cobalt symbol is Co A chemical symbol is one or two letter(s) representing an element. If the symbol is one letter, it is a printed capital. Hydrogen symbol is H If two letters, the first is a printed capital and second is lower case. Cobalt symbol is Co

Electrons Electrons are located in an electron cloud around the nucleus. There are different energy levels (“orbits” in the Bohr model) that electrons fill. 1st energy level can hold 2 electrons 2nd can hold 8 electrons 3rd can hold 18 electrons 4th can hold 32 electrons

Energy Levels of carbon atom

Fe Today’s periodic table is based on atomic number. Each element’s square contains: atomic number (protons) chemical symbol element name atomic mass (protons & neutrons) This is an average 26 Fe Iron 55.847

How to find the number of neutrons in an atom Round the atomic mass to the nearest whole number. Subtract the number of protons (atomic number). The difference is the number of neutrons. boron 10.81 atomic mass (protons + neutrons) 11 rounded - 5 atomic number (protons) 6 neutrons

Aluminum atomic mass rounded - atomic number neutrons

Gaining or losing a neutron makes an atom an isotope. Isotopes are still the same element, just more or less neutrons. carbon 12 has 6 neutrons (always 6 protons) carbon 14 has 8 neutrons (always 6 protons) The 12 refers to the mass number (protons + neutrons)

Practice calculating the number of neutrons in an atom Number a blank sheet of paper 1 to 10. Write the name for each element from the periodic table for elements 1-10. Use the right side of your paper to calculate the number of neutrons for elements 1-10. Write your answer next to the elements name.

Valence electrons are electrons farthest away Valence electrons are electrons farthest away from the nucleus (outer energy level). - involved with chemical reactions. - gives an atom its chemical characteristics. - can be shared, or transferred. - Atoms with a full valence energy level are most stable (less reactive).

hydrogen oxygen carbon neon electron dot diagram – represents the valence electrons of an element. - uses an element symbol surrounded by dots representing valence electrons. H O C Ne hydrogen oxygen carbon neon

The Periodic Table of Elements Chapter 12 Notes The Periodic Table of Elements In 1869 a Russian scientist Dmitri Mendeleev arranged elements in order of increasing atomic mass, and chemical properties. He used his table to predict properties of elements not yet discovered!

Fe Today’s periodic table is based on atomic number! Each element’s square contains: atomic number (protons) chemical symbol element name atomic mass (protons & neutrons) This is an average 26 Fe Iron 55.847

An element’s properties can be predicted by its location on the periodic table. Groups or families: vertical columns numbered 1-18. elements have similar properties Periods: across rows numbered 1-7 elements have predictably different patterns.

Metals Metals are found to the left of the stair step. Physical properties: Hardness Shininess (luster) Malleability (pound into shapes) Ductility (drawn out into a wire) Good conductors Magnetic (Co, Ni, Fe) Mostly solids at room temp.

Metals Chemical properties: wide range Some violently react with water (Na, K) Some unreactive (Au, Cr) Some corrode (react slowly with O2 and flake off) Alloys (mixture of metals) bronze (Cu + Sn) stainless steel

Metals Elements are increasingly nonmetallic reading left to right. Tend to lose electrons forming positive ions (1+, 2+) Alkali Metals Group 1 (1 valence electron) Most reactive metals! Very soft & shiny

Metals Alkaline Earth Metals Group 2 (2 valence electrons) Not as reactive as Group 1 but more reactive than most metals. Fairly hard, grey-white color Good conductors of electricity

Metals Transition Metals Groups 3-12 Fairly stable, react slowly with H2O Similar reactivity between columns Hard and shiny Good conductors of electricity

Metals Lanthanides and Actinides Called rare earth metals Fit in Periods 6 and 7 between alkaline earth metals and the transition metals. Placed below periodic table for convenience. Soft, malleable, shiny, very conductive

Nonmetals Located right of the stair step Physical properties: Most are gases at room temp. (low boiling point). dull brittle lower densities poor conductors of heat & electricity

Nonmetals Halogen Family Chemical properties: Most readily form compounds Will take electrons from metals forming negative ions (1-, 2-) Will also share electrons Many form diatomic molecules (O2, N2, H2) Halogen Family Group 17 (7 valence electrons) Very reactive! Dangerous to humans

Nonmetals Noble Gases Hydrogen Group 18 Chemically stable (unreactive) Do not gain, lose, or share valence electrons Hydrogen Alone in upper left corner Simplest element Not grouped in a family

Metalloids Along the stair step (7 elements) Have some properties of metals & nonmetals Used to make semiconductors