1. Atomic Structure Chapter 4

2. Sizing up the Atom O Radii of most atoms: 5 x 10 -11 m to 2 x 10 -10 m O Copper penny contains 2.4 x 10 22 atoms. The population of Earth is about 6 x 10 9 people. There is about 4 x 10 12 times as many atoms in a coin than people on Earth. O Line up 100,000,000 copper atoms side by side, the line would be only 1 cm long

3. Subatomic particles O Proton: positively charged subatomic particle (p + ) O Neutron: neutral subatomic particle (n 0 ) O Electron: negatively charged subatomic particle (e - ) O Protons and neutrons are the same size, but electrons are 1840 times smaller. O *All atoms are neutral* O Nucleus: tiny central core of an atom and is composed of protons and neutrons with an overall positive charge.

4. Nuclear Atom O Protons and neutrons are located in the nucleus (positive charge) O Electrons are distributed around the nucleus and occupy almost all the volume of the atom (negative charge) O The positive nucleus is balanced out with equal number or electrons. Atoms are always neutral.

5. Atomic Number O Elements are different because they contain different numbers of protons O Atomic number: number of protons in nucleus of atom O All atoms are neutral O # protons = # electrons O Blue number in upper right hand corner for each element on periodic table O Nuclear charge is the charge of the nucleus and is dependent on the number of protons.

6. Atomic Mass O The weighted average mass of atoms in a naturally occurring sample of the element O Reflects both the mass and the relative abundance of the isotopes as they occur in nature O Isotope: atoms that have same # of protons but different # of neutrons (different mass numbers) O Neon-20, Neon-21, Neon-22 O http://education.jlab.org/itselemental/iso006.h tml

7. Mass Number O Most of atom’s mass is concentrated in nucleus and depends on # protons and neutrons O Mass number: total number of protons and neutrons in nucleus of atom O # neutrons = mass # – atomic # O To determine the mass # you round the atomic mass to the nearest whole #

8. Atomic Mass Unit (AMU) O 1/12 the mass of a carbon -12 atom O More useful to compare the relative masses of atoms using a reference isotope as a standard. O Reference isotope: Carbon-12 O Helium mass = 4.00260 amu and is 1/3 the mass of carbon-12 O Table 4.3

9. To calculate atomic mass: O Multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.