Atoms and the Periodic Table

Atomic Theory Democritus (400 B.C.) Proposed that matter was composed of tiny indivisible particles Not based on experimental data Greek: atomos

Atomic Theory Alchemy (next 2000 years) Mixture of science and mysticism. Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

Atomic Theory John Dalton (1807) British Schoolteacher based his theory on others’ experimental data Billiard Ball Model atom is a uniform, solid sphere

Atomic Theory John Dalton Dalton’s Four Postulates 1. Elements are composed of small indivisible particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are different. 3. Atoms of different elements combine together in simple proportions to create a compound. 4. In a chemical reaction, atoms are rearranged, but not changed.

Atomic Theory J. J. Thomson (1903) Cathode Ray Tube Experiments beam of negative particles Discovered Electrons negative particles within the atom Plum-pudding Model

Atomic Theory J. J. Thomson (1903) Plum-pudding Model positive sphere (pudding) with negative electrons (plums) dispersed throughout

Atomic Theory Ernest Rutherford (1911) Gold Foil Experiment Discovered the nucleus dense, positive charge in the center of the atom Nuclear Model

Atomic Theory Ernest Rutherford (1911) Nuclear Model dense, positive nucleus surrounded by negative electrons

Atomic Theory Niels Bohr (1913) Bright-Line Spectrum Energy Levels tried to explain presence of specific colors in hydrogen’s spectrum Energy Levels electrons can only exist in specific energy states Planetary Model

Atomic Theory Niels Bohr (1913) Bright-line spectrum Planetary Model electrons move in circular orbits within specific energy levels

Atomic Theory Erwin Schrödinger (1926) Quantum mechanics electrons can only exist in specified energy states Electron cloud model orbital: region around the nucleus where e- are likely to be found

Electron Cloud Model (orbital) Atomic Theory Erwin Schrödinger (1926) Electron Cloud Model (orbital) dots represent probability of finding an e- not actual electrons

Atomic Theory James Chadwick (1932) Discovered neutrons neutral particles in the nucleus of an atom Joliot-Curie Experiments based his theory on their experimental evidence

revision of Rutherford’s Nuclear Model Atomic Theory James Chadwick (1932) Neutron Model revision of Rutherford’s Nuclear Model

Properties of Atoms An atom refresher Matter is anything that takes up space and has mass. All matter is made of atoms Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.

Properties of Atoms An atom refresher An atom has three parts: Proton = positive Neutron = no charge Electron = negative The proton & neutron are found in the center of the atom, a place called the nucleus. The electrons orbit the nucleus. Picture from http://education.jlab.org/qa/atom_model_03.gif

Properties of Atoms What are elements? Elements are the alphabet to the language of molecules. To make molecules, you must have elements. Elements are made of atoms. While the atoms may have different weights and organization, they are all built in the same way.

Properties of Atoms More about Elements.. Elements are the building blocks of all matter. The periodic table is a list of all of the elements that can build matter. It’s a little like the alphabet of chemistry. The periodic table tells us several things…

O Properties of Atoms Oxygen 8 16 Atomic Number: Number of protons and it is also the number of electrons in an atom of an element. 8 O Element’s Symbol: An abbreviation for the element. Oxygen Elements Name Atomic Mass/Weight: Number of protons + neutrons. 16

Properties of Atoms Atom Models There are two models of the atoms we will be using in class. Bohr Model Lewis Dot Structure

Properties of Atoms Bohr Model - The Bohr Model shows all of the particles in the atom. In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N. In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e. + + -

Electrons have special rules…. Properties of Atoms Electrons have special rules…. You can’t just shove all of the electrons into the first orbit of an electron. Electrons live in something called shells or energy levels. Only so many can be in any certain shell.

Properties of Atoms Nucleus 1st shell 2nd shell 3rd shell Adapted from http://www.sciencespot.net/Media/atomsfam.pdf

Electrons have special rules…. Properties of Atoms Electrons have special rules…. You can’t just shove all of the electrons into the first orbit of an electron. Electrons live in something called shells or energy levels. Only so many can be in any certain shell. The electrons in the outer most shell of any element are called valance electrons.

So let’s try it…. Li Lithium Protons = 3 3 7 Neutrons = 4 (7-3=4) - + Electrons = 3 2 in the 1st shell, 1 in the 2nd shell Neutrons = 4 (7-3=4)

Find the PEN and Draw Carbon P= E= N=

Find the PEN and Draw Chlorine P= E= N=

Find the PEN and Draw Magnesium P= E= N=

O Properties of Atoms Lewis Dot Structure + - The Lewis Dot Structure is a bit different from the Bohr model. It only shows the element symbol and it’s outer most electron shell. Hint: Look at the number of the group the atom is in. • O • • • • •

Properties of Atoms How to… Write the symbol. Start on the right hand side, working your way clockwise around the symbol. Try Lithium

Properties of Atoms How to… Write the symbol. Start on the right hand side, working your way clockwise around the symbol. Try Nitrogen

Properties of Atoms How to… Write the symbol. Start on the right hand side, working your way clockwise around the symbol. Try Sodium

Properties of Atoms Atom Differ by number of protons Same amount of protons and electrons, Electrically neutral Neutrons found using periodic table, usually around the same

Properties of Atoms Ion Differ by number of electrons Different amount of protons and electrons, atom with a charge Positive ion protons > electrons Negative ion protons < electrons

Properties of Atoms Isotope Differ by number of neutrons Same amount of protons and electrons Different number of neutrons, so has a different mass

Properties of Atoms

The Periodic Table of Elements 1869, Dmitri Mendeleev, a Russian chemist, set out to organize the 63 known elements. He started by organizing the elements by their mass in ascending order. When elements were arranged in order of their mass, he noticed that their physical properties repeated

The Periodic Table of Elements To group elements by similar properties, Mendeleev had to arrange a few elements out of order by mass. the periodic trends did not fit perfectly with the elements’ masses. When atomic numbers became known, scientists organized the chart of elements using the number of protons in each element instead of the atomic mass.

The Periodic Table of Elements The modern periodic table of elements is a valuable resource. Check out the wealth of information contained in the periodic table:

The Periodic Table of Elements Element name and symbol Atomic number (number of protons in each atom) Average atomic mass

The Periodic Table of Elements Physical Properties: metal, non-metal, or metalloid

The Periodic Table of Elements Electronegativity – ability to attract electrons Bigger the number, the greater the ability to attract electrons and bond to other atoms Increases as you go left to right and move up

The Periodic Table of Elements Ionization Energy – energy needed to release an electron Think, opposite of electronegativity Increases as you go left to right and up

The Periodic Table of Elements Atomic Radius Relates to number of energy levels = quantum number Increases as you go down and to the left

The Periodic Table of Elements Valence Electrons – outermost electrons Elements in the same group have similar valence electrons

The Periodic Table of Elements Oxidation Number – number of electrons the atom uses or receives + when atom loses electrons, - when atom gains electrons

The Periodic Table of Elements Representative Elements Columns 1-2 and 13-18 Follow trends and behave more predicatibly than other groups

The Periodic Table of Elements Exception to the Rules Hydrogen Placed with metals even though it is a gas Placed in 1st column to reflect the properties of its electrons