# Make any needed corrections with a RED pen! Work quietly with your group!

## Presentation on theme: "Make any needed corrections with a RED pen! Work quietly with your group!"— Presentation transcript:

Make any needed corrections with a RED pen! Work quietly with your group!

Helium has 2 protons (2+) & 2 electrons (2-), so charges cancel each other Because water is polar: B/c they have the same number of protons and electrons (+ and – charges)

Why are elements (like Helium) neutral? Protons = 2+ Electrons = 2- 0 The positive & negative charges are equal so they cancel each other out. (neutral)

Water Molecule Water is Polar : One end is positive (+), the other end is negative (-) - + Simplified Drawing:

Why? Because water is a polar molecule! - It’s attracted to both positive AND negative charges H H O

Why does water bend towards the charged object when the objects have different charges? Glass is positively charged, so it attracts negative end of water. Knife is negatively charged so it attracts positive end of water. - + Water is Polar! Charged comb (negatively charged) - - -

Comb “steals” electrons from hair and becomes negatively charged. e-e- e-e- e-e- This leaves your hair with an overall positive charge, so hair is attracted to comb because opposite charges attract! The Van de Graff generator gives off e- and gives your hair negative charges.!

Atom model evolved from a very simple “sphere” to much more complex, including subatomic particles (protons, neutrons, electrons) and has them in specific places. Why? Because of new research!

INDIRECT b/c scientists can’t “see” an atom. All of their inferences are based on indirect evidence Atoms have a very small nucleus (center of atom) Nucleus is positively charged (protons) Atoms are mostly empty space

1911

Electron Energy Levels nucelus 1 st energy level 2 nd energy level 3 rd energy level 1999, Addison, Wesley, Longman, Inc. Energy absorbed e- fall back = Energy Released (what we see as colors) = e- jump Niels Bohr: Bohr Model – showed e - exist ONLY in specific energy levels (shells)

Electrons “falling” from higher (“excited”) to lower (“resting”) energy level. Energy levels (“orbits”) where electrons cannot go. Electrons! Red (=LOW energy, but longer wavelength) Violet (= HIGH energy, but shorter wavelength)

Some elements have many different e - energy levels, other elements have fewer:

Test is next class. STUDY. Open up the book and read the page, open up the book and get an A….

A little more Chemistry Humor: