Atoms & Atomic Bonds 9/30 OBJECTIVES: TASKS: Define atomic bond, chemical reaction, and ion. Explain what causes chemical reactions. TASKS: 1. Classify the following as elements, compounds, atoms, or molecules: a. A gold (Au) nugget b. The smallest piece of water (H2O) possible. c. A glass window (SiO2) d. The smallest piece of sodium (Na) possible 3. Draw a quick sketch of a He atom, with 2 protons, 2 neutrons, and 2 electrons.

Answers A gold nugget is an element, since it is made of many gold atoms (and only gold atoms!) The smallest piece of water is a single water molecule. Any smaller than that, and it’s not water! SiO2 (glass) is a compound, since it is made up of several types of atoms joined together. [note: the smallest piece of glass possible would be a single molecule of SiO2] Since sodium (Na) is an element, the smallest sample possible is a single sodium atom.

Parts of an atom: Label the diagram Atoms contain 2 parts: The atomic nucleus contains protons and neutrons Electrons fly around the nucleus near the speed of light

What Atoms are made of Atoms are made of 3 parts. Protons are found in the atomic nucleus. They have a positive electrical charge. Neutrons are also found in the atomic nucleus. They have no charge. Electrons are found outside of the nucleus. They have a negative charge.

Atom’s radius = 170 pm Nucleus’ radius = 0 Atom’s radius = 170 pm Nucleus’ radius = 0.0027 pm 105 = 5 orders of magnitude. Fruit Fly length = 0.002 m Camden Yard’s radius = 150 m 105 = 5 orders of magnitude.

Different Elements = Different Atoms Atoms of different elements are different from one another because they have different numbers of protons, neutrons, and electrons.

Atomic Number The atomic number is the number of protons in an atom’s nucleus. The nuclei of atoms do not change, except in nuclear reactions (fission, fusion, radioactivity) In a neutral atom (charge = 0), there are equal numbers of positive protons and negative electrons. If atoms gain electrons they become negative, and if they lose electrons, they become positive.

Charges? Ions – Atoms with electrical charges (either + or -) What’s the charge of an atom with… 1 electron, 1 proton? 5 electrons, 5 protons? 1 electron, 2 protons? 2 electrons, 1 proton?

Atomic Bonds [aka chemical bonds] What is a bond? So what is an atomic bond? An attractive force between 2 atoms.

What causes atomic bonds? When atoms change how they are bonded to one another, that is called a chemical reaction. Why do chemical reactions happen?

What’s more likely? Things go from high energy to low! Water flowing down a cliff to make a waterfall… or water flowing up? Falling down a flight of stairs or falling up? Dropping an egg and making a mess or dropping a broken egg and getting one that’s back together?

It’s all about Potential Energy Atoms bond to get a lower energy configuration. Arrows indicate increasing potential energy

But Why? ELECTRONS DETERMINE HOW ATOMS BOND Atoms that have a full outer energy level are very stable. This is the driving force of bonding reactions. Atoms bond together in a way that fills their outermost electron energy level. (2 or 8) This is the lowest energy configuration possible.

It’s all about Energy 2-8-1 Not Stable Ne Ne Ne 2-7 Not Stable 2-8 VERY Stable

Recap Atomic bond: attraction between two atoms Ion: atom with an electrical charge Chemical reaction: occurs when atoms break and/or form new bonds

For Tonight HOMEWORK: Follow Syllabus