Chapter 5 section 1 models of the atom

So far we have 3 atomic models, or what the atom looks like Dalton – small round sphere, that is indivisible and indestructible. We now know due to the hydrogen bomb research in the 40s that we can divide atoms. JJ Thomson – still small and spherical shape, but the whole atom has a positive charge the balance the negative electrons inside the atom. Rutherford – small but protons and neutrons are in a small center, called the nucleus, and the electrons orbit the nucleus.

Rutherford’s model didn’t explain most chemical properties of atoms. Rutherford‘s model couldn’t explain why metals when heated give off a certain color of light or why objects like, metal, when heated to higher temperatures go through a color change: red, yellow, then white

Bohr’s atomic model Niels bohr was a student of Rutherford. In 1913 Bohr changed Rutherford’s model to explain how the energy of an atom changes when it absorbs or emits light.

Niels Bohr atomic model his model proposed that an electrons are found in a specific circular path, or orbits, around the nucleus

Bohr states that each electron has a fixed orbit with a fixed energy Bohr states that each electron has a fixed orbit with a fixed energy. The fixed energy can be different for each electron, they have their own energy levels.

The lowest energy level is closest to the nucleus. Each energy level increases in energy the further away from the nucleus. Energy levels are not equal distance from each other, the higher energy levels are closer together

Bohr also stated that electrons can only exist in the energy levels, not between levels He said that electrons can change energy levels by gaining or losing a specific amount of energy

In order for an electron to move, bohr states that energy must be gained or lost by the electron, the amount of energy an electron gains or loses is called, a quantum of energy.

Bohr model energy gain and loss on board

Electrons as waves Bohr’s atomic model explained electron behavior very well in gasses but his model did not work to explain electron behavior in all atoms. Because of the photoelectric effect and the line spectrum of hydrogen, light has a dual wave/particle nature Electrons are thought to behave the same way

Electrons as waves Louis de Broglie, a French scientist, proposed that electrons could have the same dual wave/particle nature. Sometimes the electron has wavelike properties and sometimes it has particle properties.

Electrons as waves De Broglie suggested the electrons be considered waves confined to the space around the nucleus.

Electrons as waves De Broglie and others confirmed through experiments that electrons can be bent(diffracted) and can experience interference.

Heisenberg uncertainty principle Werner Heisenberg, german, theoretical physicist Questioned electrons as waves and particles. If this was true, where are the electrons located in the atom?

Heisenberg uncertainty principle Heisenberg uncertainty principle - proposed that it is impossible to determine simultaneously both the position and velocity of an electron Because of this it has been proven to be one of the fundamental principles of our understanding of light and matter

Because of schrodinger, Heisenberg, and de Broglie and other scientists Electrons are now thought to be in regions, not specific orbits. These regions are called orbitals Orbitals are three dimensional regions around the nucleus that indicate the probable location of an electron

orbitals There are 4 orbital shapes S p d f

S orbitals

P orbitals

D orbitals

F orbitals

S orbitals Sphere shape Maximum of 2 electrons in each shape

P orbitals Dumbbell shape Maximum number of electrons in each shape – 2 Total electrons in the p orbitals – 6

D orbitals Maximum number of electrons each shape – 2 Total number of electrons for the d orbitals - 10

F orbitals Maximum number of electrons per shape – 2 Total number of electrons for f orbitals - 14

Orbital blocks on periodic table

We can use the periodic table to help us find the electron locations in elements atoms

Electron configuration Electron configuration is a way of writing where each of an element’s electrons are located in the atom Example: O is in the second energy level and has 8 electrons In the first energy level there are 2 electrons in a s orbital In the second energy level that are 2 electrons in a s orbital and 4 electrons in a p orbital We would write this as 1s22s22p4

Electron configuration for oxygen ( 0 ) energy levels 1s22s22p4 number of electrons orbital shapes

Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. Principal quantum number Angular momentum quantum number Magnetic quantum number Spin quantum number

Principal quantum number Symbol – lower case n Indicates the main energy level of the electrons N=1 1st energy level n=4 n=7 N=2 2nd energy level n=5 N=3 3rd energy level n=6

Angular momentum quantum number Symbol – lower case cursive l Indicates the shape of the orbital L=0 s shape L=1 p shape L= 2 d shape L= 3 f shape

Magnetic quantum number Symbol – lower case m Indicates the orientation of an orbital around the nucleus M = 0 s orbital M= -1, 0, +1 p orbital M = -2, -1, 0, +1, +2 d orbital M = -3,-2,-1,0,+1,+2,+3 f orbital

Spin quantum number Symbol is 1 2 or - 1 2 Indicates the two spins of electrons, positive or negative

Number of electrons in each energy level and their orbitals Energy level orbital number of max electrons 1 S 2 2 S 2 8 2 P 6 3 S 2 3 P 6 18 3 D 10