© 2004 Pearson Education Inc., publishing as Addison-Wesley

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

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

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

Hydrogen Deuterium isotope p+ e- n 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) = 1.602x10-19 J =0.0000000000000000001602 J This is because atomic energies are incredibly small… for a typical football player:

Hydrogen … En = -13.6 / n2 n En (eV) 1 -13.60 2 -3.40 3 -1.51 4 -0.85 1 -13.60 2 -3.40 3 -1.51 4 -0.85 5 -0.38 … n=1 n=4 n=3 n=2 En = -13.6 / n2

What if an electron is missing? ion e- p+ p+ n n atomic number = 2 4 2 He+1 atomic mass number = 4

What if two or more atoms combine to form a particle? molecule p+ p+ 8p+ 8n H2O (water)

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 -0.85 eV -1.51 eV -3.40 eV -13.60 eV

Hydrogen … … En = -13.6 / n2 n En (eV) 1 -13.60 2 -3.40 3 -1.51 1 -13.60 2 -3.40 3 -1.51 4 -0.85 5 -0.38 … Ground state 1st excited state 2nd 3rd 4th n=1 n=4 n=2 n=3 … En = -13.6 / n2

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

Important years for astronomy Levoisier 1789; mendeleev 1869; Rydberg 1888

En = -13.6 / n2 (eV) (Rydbergs formula) … n En (eV) 1 -13.60 2 -3.40 3 -1.51 4 -0.85 5 -0.38 … En = -13.6 / n2 (eV) (Rydbergs formula) DE(3 g 2) = E3-E2 =-1.51-(-3.40) = 1.89 eV

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/s2]

As objects fall, they accelerate. The acceleration due to Earth’s gravity is 10 m/s each second, or g = 10 m/s2. 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 You may remember my experiment…

The Acceleration of Gravity (g) Galileo measured g to be about 10 m/s2 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!

Universal Laws of Motion “If I have seen farther than others, it is because I have stood on the shoulders of giants.” Sir Isaac Newton (1642 – 1727) Physicist

Sir Isaac Newton (1642-1727) Perhaps the greatest genius of all time Invented the reflecting telescope Invented calculus Connected gravity and planetary forces Philosophiae naturalis principia mathematica

Forces acceleration Forces change the motion of objects. As long as the object’s mass does not change, the force causes a change in velocity, or an… acceleration

Newton’s Laws of Motion # 1 A body at rest or in motion at a constant speed along a straight line remains in that state of rest or motion unless acted upon by an outside force.

Newton’s Laws of Motion # 2 The change in a body’s velocity due to an applied force is in the same direction as the force and proportional to it. The proportionality constant is mass: F a a F = m a

Gravity: F = mg g is the gravitational acceleration (9.8 m/s2)

Gravitational Potential Energy E = F n h = mg n h m g h

Newton’s Laws of Motion # 3 For every applied force, a force of equal size but opposite direction arises.

Newton’s Laws of Motion

Is Mass the Same Thing as Weight? mass – the amount of matter in an object weight – a measurement of the force which acts upon an object When in “free-fall,” you are weightless!!

momentum – the (mass x velocity) of an object Forces Forces change the motion of objects – cause accelleration. momentum – the (mass x velocity) of an object p = mv [kg m/s] force – anything that can cause a change in an object’s momentum F = D(mv) = mDv = ma [kg m/s2 =N]

Escape velocity ! Can an object escape the gravitational attraction of the Earth? Does it have enough kinetic energy to overcome the gravitational potential energy of the Earth? mgh I ½ mv2 ????