The Development of the Atomic Theory Atomic Theory and Models

Development of the Atomic Theory Person: Democritus Idea: Discovered the atom

Development of the Atomic Theory Person: John Dalton Idea: Published an atomic theory

Development of the Atomic Theory Person: JJ Thomson Idea: Discovered electrons

Development of the Atomic Theory Thomson’s Plum-Pudding Model…

Development of the Atomic Theory Person: Ernest Rutherford Idea: Discovered protons

Development of the Atomic Theory Person: Niels Bohr Idea: Electrons move in energy levels

How small is an atom? A penny is made up of 20,000,000,000,000,000,000,000 atoms of copper and zinc. That’s 20 thousand billion billion atoms!

Protons—positively charged particles in the nucleus (+) Even though atoms are very small, they are made up of even smaller things. Protons—positively charged particles in the nucleus (+) Neutrons—particles of the nucleus that have no electrical charge (neutral) Electrons—negatively charged particles outside the nucleus (-)

Use this to draw your own diagram of an atom: Electron Cloud Neutron Electron Nucleus Proton

The nucleus is very dense. It contains protons and neutrons.

Electrons are found on electron clouds…outside the nucleus. Electrons are very small in mass. It takes more than 1,800 electrons to equal the mass of one proton. The mass of an electron is so small that it is usually thought of as almost zero.

Atoms have no charge. That means they’re neutral. Atoms have no overall charge. The protons (+) and electrons (-) cancel each other out. Example: Hydrogen = 1 proton + 1 electron If an element has 3 protons…it should also have 3 electrons.

How can you tell how many protons are in an atom of a given element? Atomic # vs. Mass # How can you tell how many protons are in an atom of a given element? Use the Periodic Table…look at the atomic #. Atomic Number—the number of protons in the nucleus of an atom…and it also tells you how many electrons it has All atoms of an element have the same atomic number. Example: Every hydrogen atom has an atomic # of 1. Every helium atoms has an atomic # of 2.

Atomic Number So…every Cobalt atom has 27 protons. And…if it has 27 protons, it also has 27 electrons.

Now you try… Using the periodic table, find the atomic number for the following elements: Nickel Calcium Lithium 28 20 3

Now, let’s determine how many neutrons are in each element. Mass Number—number of protons and neutrons in the nucleus of an atom (Atomic Mass) Round 58.6 to 59. then… 59 - 28 31 Mass #

Atomic Mass Number

Atomic # vs. Mass #

Now you try… How many protons, neutrons, and electrons? 3 protons, 4 neutrons, 3 electrons Lithium 1 proton, 0 neutrons, 1 electron Hydrogen 4 protons, 5 neutrons, 4 electrons Beryllium Helium 2 protons, 2 neutrons, 2 electrons

Determine the number of protons, neutrons, and electrons in the following…

What is an isotope? Isotope—two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons (same atomic #; different mass #)

CLASSIFYING ELEMENTS Elements are pure substances, meaning it can’t be simplified. Elements are made from only one type of atom. Example: Carbon is only made from carbon atoms. Hydrogen is only made from hydrogen atoms. Water is made from hydrogen and oxygen atoms so water is not an element. (It’s a compound.)

Atoms of a specific element are the same no matter where they’re found.

Elements have properties. EXAMPLES: color, shininess, boiling point, melting point, density, flammability, malleability, ductility…

Classifying Elements Elements are classified (grouped together) based on their similar properties. Metals—shiny; conducts heat and electricity well, malleable, ductile Nonmetals—the solids are dull and brittle; conducts heat and electricity poorly Metalloids (or semi-conductors)—have properties of both metals and nonmetals

Classifying Elements Metals Nonmetals Metalloids

Molecules A molecule is a group of atoms (2+) that are bonded together. Common examples include oxygen gas, hydrogen gas, methane gas, water, carbon dioxide, carbon monoxide, and glucose.

How many water Molecules? 5

How many carbon dioxide Molecules? 3

How many Hydrogen gas Molecules? 6