The Atom

..\Video download\Tsar Bomba REMASTERED.mp4

In the beginning… Atoms are the basic building blocks of matter. The word atom is derived from the Greek word atomos, which means indivisible or uncuttable.

The Greeks concluded that matter could be broken down into particles too small to be seen. These particles were called atoms.

How Small is an Atom? The average size atom (Al) is about 0.00000003 cm. It would take a stack of 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil.

There are over 6,000,000,000,000,000,000,000 (6 x 1021) atoms in one drop of water. It would take you about 100 trillion years to count this number out.

 It would take you 500 years to count the number of atoms in a grain of salt.

If we stretched a penny until it covered the entire US, each of its atoms would be only 3 cm across!

Atomic Structure

Atomic Structure Atoms have 3 main parts, called subatomic particles.

Atomic Structure Nucleus: (center of atom) 1. Protons have a positive (+) charge 2. Neutrons have no charge, they are neutral

Atomic Structure (cont’d) Orbitals: (shells, cloud, flying around outside) 3. Electrons have a negative (-) charge

Atomic Structure

These things are teeeeny tiny The mass of a proton is really small, so small in fact, that scientists created a whole new unit for it. A proton has a mass of 1 atomic mass unit (AMU).

Atomic Mass Unit (AMU) The unit of measurement for an atom is an AMU. It stands for atomic mass unit. One AMU is equal to the mass of one proton.

Atomic Mass Unit (AMU) There are 6 X 1023 or 600,000,000,000,000, 000,000,000 amus in one gram. (Remember that electrons are 2000 times smaller than one amu).

A neutron is actually a little bigger than a proton, but not enough to notice the difference, so we say it also has a mass of 1 AMU.

Electrons are so small, they don’t have a measurable mass.

1 amu p+ 1 amu 0 amu Nucleus Positive Nucleus Neutral Outside in Shells 0 amu Negative

Atomic Number is the Number of Protons All 112 elements are made of atoms.

What makes the elements different? The atomic number, or number of protons, determines the element. Example: Every gold atom has 79 protons.

Key to the Periodic Table Elements are organized on the table according to their atomic number, usually found near the top of the square. The atomic number refers to how many protons an atom of that element has. For instance, hydrogen has 1 proton, so it’s atomic number is 1. The atomic number is unique to that element. No two elements have the same atomic number.

What’s in a square? Atomic Number Chemical Symbol Atomic Mass Name State of Matter “Color of symbol” Metal, nonmetal or metalloid “color of box”

Protons? 4 81 17 108 27 13

When is an atom neutral? An atom is neutral when it has an equal number of electrons and protons. Example: Helium has 2 protons & 2 electrons That means it has 2 + charges & 2 - charges. They cancel to create no charge.

How Many Electrons? 74 12 16 68 36

Atomic number also equals the number of electrons.

How do you find an atom’s mass? What are the only two parts of an atom that have mass? Protons have a mass of 1 amu Neutrons have a mass of 1 amu Electrons are so teeny they don’t weigh anything.

Atomic Mass/Mass # Mass Number = number of protons + number of neutrons You Try

5 5 6

18 18 22

3 7 3 3 4 Boron 11 6

Think About This! 1. What is heavier, an atom’s nucleus or the orbitals? Nucleus 2. What happens to an atom that has an extra neutron? It becomes a heavy Isotope 3. What happens to an atom that is missing an electron? It becomes a charged ion

Questions... What particles are in the nucleus? Explain why atoms are neutral. Why do scientists say that most of the mass of an atom is located in the nucleus?

How Do Atoms of Different Elements Differ? Lets compare a Hydrogen atom and a Helium atom…

Hydrogen... Draw one proton. Draw a circle around the proton. Place one electron on the circle. You have just created a hydrogen atom! Hydrogen has no neutrons.

H DOT & CROSS DIAGRAMS Hydrogen - With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; Hydrogen H 1 - Electron (-) 1

Helium Draw two protons and two neutrons all together. Draw an electron orbit around them. Place two electrons on the orbit. You have just created a helium atom!!!

Helium - + N 2 - He N + Electron (-) 4

HELIUM ATOM + - + - Shell proton neutron electron What do these particles consist of?

Bohr’s Atom electrons in orbits nucleus

What is different? The two different elements have different numbers of electrons, protons, and neutrons. OK...

Are all atoms of an element the same? Draw another Hydrogen atom, but this time add a neutron. It is still Hydrogen because it has only one proton, but it has more mass in the nucleus. It is called an isotope.

What is an Isotope? Isotope - atoms that have the same number of protons but have different numbers of neutrons. Some isotopes are radioactive. Otherwise they are mostly the same as the regular atom.

How can you tell one isotope from another? By their mass numbers. mass number = protons + neutrons. Different isotopes will have different mass numbers because they have different numbers of neutrons.

Let’s see... Hydrogen-1 has 1 proton and 0 neutrons. Mass Number = 1

Questions… List the charge, location, and mass of each particle. Determine the number of protons, electrons, and neutrons in aluminum-27.