CHEMISTRY

Atoms, Elements & the Periodic Table Describe the structure & parts of an atom. Identify the properties of an atom. Interpret information on a periodic table to understand how elements are grouped.

What are the elements made of? Element-the simplest pure substance. Elements are made of atoms, and each element’s atoms are unique to that element Atoms-the basic building blocks of all matter. They are the smallest particles into which an element can be divided and still be the same substance. Atoms are made of 3 types of particles-protons, neutrons and electrons

The History of Atomic Theory

Democritus – 440 BCE Greek Philosopher 2445 years ago. Called particles that made up “stuff” ATOMS Atomos (Greek word) “not able to be divided”(uncuttable) small hard particles Constantly move

Dalton - 1803 Atoms make up all substances (the elements) Atoms can not be created, divided or destroyed. Atoms combine to make other substances. Conducted experiments

Dimitri Mendeleev Proposed the laws of the periodic table 1869-developed the first periodic table Table was arranged according to increasing atomic weight Left spaces for elements yet to be discovered

J.J. Thomson - 1897 Discovered negatively charged particles in atoms called Electrons. Conducted Cathode Ray Tube experiment Led to the Plum Pudding Model

Ernest Rutherford - 1909 Discovered the nucleus Nucleus Small tiny very dense center of atoms Where most the atoms mass is located Atoms are mostly empty space where electrons are found Conducted the Gold Foil experiment

Niels Bohr - 1913 Electrons move around the nucleus of atoms in definite paths. Electrons jump between levels from path to path. Bohr’s model

Most Recent Atomic Theory Schrodinger and Heisenberg Electron paths cannot be predicted. Electrons are likely to be found in regions around the nucleus called electron clouds. Called the electron cloud model.

Recent Discoveries Chadwick 1932-Discovered that neutrons exist in the nucleus of atoms Neutrons have no charge and the mass equal to protons and help to stabilize the atom Gell-Mann 1969-Subatomic particles are made of smaller particles called quarks

PERIODIC TABLE =ORGANIZED ELEMENTS Elements are: PURE-Made of like atoms of that element Identified by it’s atomic number (# of protons) Arrangement of electrons determines the elements properties (such as conductivity and reactivity).

The Element Song Link to video http://www.privatehand.com/flash/elements7.swf Select broadband player.

The Structure of an Atom Protons – POSITIVE charged particles inside the nucleus (center). Neutrons – neutral particles inside the nucleus that have NO CHARGE! Electrons – NEGATIVE CHARGED particles in atoms found around the nucleus.

Atomic Particles Location Charge Mass Protons Nucleus + positive Heaviest particle Neutrons O Neutral Similar to a proton but carry no charge Electrons Orbiting outside the nucleus in electron clouds - Negative Lightest particle Smallest part of an atom

Outside the nucleus Can be called a electron cloud, shell, energy level, orbit or ring Area outside the nucleus where electrons are found 1st cloud=2 electrons 2nd cloud=8 electrons 3rd cloud=18 electrons

Boron (B) Atomic #=5 Atomic Mass=11 Protons=5 Neutrons=6 Electrons=5

Sodium-(Na) Atomic #=11 Atomic Mass=23 Protons=11 Neutrons=12 Electrons=11

Energy Levels - Electron Clouds Regions around the nucleus where electrons are arranged. Electrons further away from the nucleus have more and more energy. Each level or cloud can hold a specific # of electrons. 1st level - 2 electrons 2nd level - up to 8 electrons 3rd level-up to 18 electrons

Valence Electrons The electrons in the outermost energy level (electron cloud). Very important because they determine how an element will react with other substances

What’s in the Box?

Atomic Number 5 B 10.81 Boron Equals the number of protons inside the nucleus of the atom. Atomic Number=Number of Protons=the number of electrons Determines the element. All atoms of an element have the same atomic number. No two elements have the same atomic number.

Symbol B All elements have their own unique symbol 5 B 10.81 Boron All elements have their own unique symbol Symbols can be one or two letters The first letter is always a capital letter The second is always a lower case letter Symbols don’t always match their English word bc most are from Latin or Greek roots. Example: Fe=Iron (English) Ferrum (Latin)

Mass Number 5 B 10.81 Boron The total number of protons and neutrons in an atoms nucleus. Number under the element symbol Protons + Neutrons = Mass Number Practice: If an atom has 12 protons, 14 neutrons and 12 electrons, what is its mass number? Practice online Ans: 12 protons + 12 neutrons=24

Atomic Mass Unit - amu Unit of measurement for the mass of subatomic particles. 1 amu = 1.7 X 10 -24 They are TEENY TINY!!! .000000000000000000000017 grams Proton = 1 amu Neutrons = 1 amu Electrons = almost zero (TINIEST particle with the least mass) Most of the mass is in the nucleus with protons and neutrons Otherwise atoms are mostly EMPTY SPACE Amu will be addressed in slide 14, but you can refer back to this slide for review at the end

Atomic Mass Refers to the weight of the atom. Atomic Mass= Protons + Neutrons Never negative Mass

The Charge of an atom To find the charge of an atom- Find the number of protons (+) Find the number of electrons (-) Represent the electrons as a negative number Add the protons and electrons to find the charge Ex: Calcium atom has 12 protons and 10 electrons. What is the charge of this atom? Answer 12 proton + 10 electrons 12 + (-10)= +2 This atom would be positive (+) Be sure to reinforce that these are not neutral atoms. When students look at their periodic table, they can assume all of the elements’ atoms are neutral unless given additional information. Also point out that the only thing to change the charge is whether the atom has gained or lost electrons, and that the # of protons will always stay the same. The method above is designed to help students avoid thinking “the atom LOST electrons, so it must be negative, “ and lets them use simple math

More practice with charge What is the charge of a copper atom with 26 electrons? What is the charge of a Sulfur atom with 18 electrons? 29 protons (+) + 26 electrons (-) 29-26=+3 positive Copper’s atomic # is 29 if students do not have their periodic table 16 protons (+) + 18 electrons (-) 16-18=-2 negative

Review Nucleus-contains protons and neutrons Electron Cloud-electrons orbit the nucleus Elements are made of Atoms, which contain Protons (+), neutrons (o)and electrons (-) #protons # neutrons Mass #

Periodic Table Overview

How the Elements are Arranged Groups/Families: Similar properties Periods/Rows: Increasing atomic number/mass

Groups/Families Columns of the periodic table that consist of elements that have the same number of valence electrons. Groups 1 and 2 - same # as group Groups 13-18 - 10 - the group # Groups 3-12 - no general rule.

Periods Rows of the periodic table that consist of elements with the same number of electron clouds or energy levels.

Alkali Metals Group #1 All metals 1 Valence Electron Very reactive

Alkaline-Earth Metals Group #2 All Metals 2 Valence Electrons Very reactive but less than group #1.

Transition Metals Groups # 3-12 All metals 1-2 valence electrons Less reactive than group #2 Also contain lanthanide and actinide series (radioactive/unstable).

Groups # 13-16 Elements change from metals to nonmetals and include the metalloids. Atoms have 10 fewer valence electrons than the group #. Boron Group #13 - 3 valence electrons Carbon Group #14 - 4 valence electrons Nitrogen Group #15 - 5 valence electrons Oxygen Group #16 - 6 valence electrons

Halogens Group 17 All nonmetals 7 valence electrons Very reactive Only need to gain 1 more electron.

Noble Gases Group # 18 All nonmetals 8 valence electrons - except helium only has 2. Unreactive Have a full outer electron cloud (energy level).

Hydrogen stands alone 1 valence electron Very reactive Reacts violently with Oxygen under the right conditions.

Everyday Uses

Isotopes Atoms of elements that have the same number of protons (atomic number) but a different number of neutrons inside the nucleus.

Ions Charged particles that form during chemical changes. Form when one or more valence electrons are transferred from one atom to another.

Ions are Charged! + or - Atoms that lose electrons become positive ions. Atoms that gain electrons become negative ions. Cl gains an electron from Na to form NaCl - Cl ion is negative - more electrons (-) Na ion is positive - more protons (+).