© 2004 Pearson Education Inc., publishing as Addison-Wesley Anyone planning to take the Astro 300 Lab in the fall?

Atom nucleus electron proton neutron e-e- p+p+ n An atom consists of a small, dense nucleus surrounded by electrons

The “size” of an Atom Although it is the smallest part of the atom, most of the atom’s mass is contained in the nucleus. The electrons do not “orbit” the nucleus; they are “smeared out” in a cloud which give the atom its size.

Hydrogen atomic number = 1 atomic mass number = 1 e-e- p+p+

e-e- e-e- Helium p+p+ nn p+p+ atomic number = 2 atomic mass number = 4

Hydrogen e-e- p+p+ n Deuterium isotope atomic number = 1 atomic mass number = 2

The particles in the nucleus determine the element & isotope.

atomic number = #protons atomic mass no. = #protons + #neutrons

Note on Energy on Atomic Scales: We use a smaller unit of Energy on quantum scales.. The electron-volt (eV) = 1.602x J = J This is because atomic energies are incredibly small… for a typical football player:

n=1 n=2 n=3 n=4 n E n (eV) … … E n = / n 2 Hydroge n

p+p+ n e-e- n p+p+ atomic number = 2 atomic mass number = 4 What if an electron is missing? ion He

What if two or more atoms combine to form a particle? p+p+ 8p + 8n molecule H 2 O (water) p+p+

Phases of Matter the phases –solid –liquid –gas –plasma depend on how tightly bound the atoms and/or molecules are As temperature increases, these bonds are loosened:

Phases of Matter the phases –solid –liquid –gas –plasma depend on how tightly bound the atoms and/or molecules are As temperature increases, these bonds are loosened:

Electron Energy Electrons that are bound in atoms can gain or lose energy. When electrons have the lowest energy possible, we say the atom is in the ground state. When electrons have more energy than this, the atom is in an excited state. When electrons gain enough energy to escape the nucleus, the atom is ionized.

Electron Energy Levels Electrons can not have just any energy while orbiting the nucleus. Only certain energy values are allowed. Electrons may only gain or lose specific amounts of energy. Each element (atom and ion) has its own distinctive set or pattern of energy levels. This diagram depicts the energy levels of Hydrogen. 0.0 eV eV eV eV eV

n=1 n=2 n=3 n=4 n E n (eV) … … E n = / n 2 Hydroge n Ground state 1 st excited state 2 nd 3 rd 4 th …

n=2 n=3 Photons are created when an electron jumps from one energy level to another

n E n (eV) … … E n = / n 2 (eV) (Rydbergs formula)  E  3  2  = E 3 -E 2 =-1.51-(-3.40) = 1.89 eV

Important years for astronomy

Objects in Motion speed – rate at which an object moves, i.e. the distance traveled per unit time [m/s; mi/hr] velocity – an object’s speed in a certain direction, e.g. “10 m/s moving east” acceleration – a change in an object’s velocity, i.e. a change in either speed or direction is an acceleration [m/s 2 ]

As objects fall, they accelerate. The acceleration due to Earth’s gravity is 10 m/s each second, or g = 10 m/s 2. The higher you drop the ball, the greater its velocity will be at impact.

You may remember my experiment… t=0s; v=0m/s t=1s; v=10 m/s t=2s; v=20m/s

The Acceleration of Gravity (g) Galileo measured g to be about 10 m/s 2 He demonstrated that g is the same for all objects, regardless of their mass! This was confirmed by the Apollo astronauts on the Moon, where there is no air resistance. Galileo was right!