Chemistry: The Structure of Atoms

Electromagnetic Spectrum

According to this principle: Infrared(heat energy), Microwave, and radiowave have long wavelength; therefore, they have shorter frequency and low energy. On the other hand, Visible light( various colors), ultraviolet, X-ray, and Cosmic rays have shorter wavelength, high frequency and high energy. However, all of them have the same speed. Gamma ray has the shortest wavelength, meaning the highest frequency and energy

The Quantum Mechanical Picture of the Atom

Previously: 1.Albert Einstein studied the Photoelectric Effect and concluded that light behaves as if it were of tiny packets of energy called photons(E=hv) 2.N.Bohr concluded that only certain levels of energy are possible( his orbitals around the nucleus) 3.L. de Broglie concluded that very small particles such as electrons also display the properties of wave. Since classical mechanical could not solve problems dealing with very small particles, a different approach was needed, call quantum mechanics, based on wave properties of matter! Some of the Principles: a. Heisenberg uncertainty Principle of 1927 - he concluded that is not possible to know the position of a particle and momentum accurately at the same time- Only the probability could be determine b.Atoms and molecules can exist only in certain energy states. Electron must be in one of these states, not in between. c.Atoms and molecules emit or absorb radiation as they change their energy levels. d. The energy states can be described by a set of quantum number. Each electron has its own unique set of quantum number! e. Schrodinger(1926) Quantum number: -Principle quantum number, n, describes the main energy level or the "electron shell''. Its values can be 1,2,3,4,5,6,7 -Angular momentum quantum number ,L, tells the shape of region in space where is a probability that the electron is located. L=o,1,2,...(n-1) -Magnetic quantum number, m_L tells the orientation in space. Allowed values of m_l = -L...0... +L -Spin quantum number,m_s, is the spin of an electron. Only 2 values for m_s = +1/2, -1/2

H.G.J. Moseley

Was a remarkable scientist who worked with Ernest Rutherford. In 1913 as a young graduate student, he studied X-rays given off by different pure element and concluded that "Each element is different from preceding element by having 1 more positive charge in the nucleus." This means as the elements move across the periodic table, the atomic number/ mass # increases by one.

Summary

n-tells the electron shell/periods/energy levels (n=1,etc) L-tells the shape of orbit(l=0,...n-1) L=0 have a spherical ''s'' shape L=1 have a dumbbell ''p'' shape L=2 have a cloverleaf ''d'' shape L=3 is ''f'' complex shape m_l tells direction in space, can be -L...0...+L How are electrons placed in orbitals? a. Aufbau Principle fill orbitals in order of increasing energy Pauli Exclusion Rule Principle- no two electrons can have the same four quantum # Hund's Rule - degenerate orbitals are 1/2 filled before pairing paramagnetic- have unpaired electrons Diamagnetic-paired electrons

Study of Light

1. light is a form of energy known as electromagnetic radiation( which is basically something give off by another). Properties of Waves: -Wavelength known as lambda measured in meters .On a wave, is the distance from crest to crest -Frequency is how many waves crest passed by as you observe in a given time. .Units: cycles per second, per second, or hertz Fundamental relationship: C=lambda multiply by frequency, C is the speed of light which equal 3E8 m/s Light also has some properties of matter. Max Planck in the 1900 and Albert Einstein in 1905 found that light behave like tiny packets of energy called ''Photon" Planck then came up with an equation called Planck's Equation: E=hv or change in energy = hv=hc/lambda h is Planck's constant =6.626E-34 j.s

The fundamental particles that make up an atom

1. proton, proton is the atomic number. Also, both proton and electron have the # -has a electrical charge of +1 esu -has a mass of 1 amu and is located in the nucleus 2. Electron: -has a electrical charge of -1 esu -has a mas of 0 amu and is located in the electron cloud 3. Neutron: -has a electrical charge of 0 amu - mass of 1 amu and is located in the nucleus # of neutron = Atomic #- # of atomic mass

The atomic weight Scale/Atomic weights

1.Atomic weight scale is based on the mass of 12C6 isotope. 2.One amu is exactly 1/12 weight of 12C6 3. 1gram =6.02 x 10^23 amu The atomic weight of an element is the weighted average of masses of all isotopes. Summary: Atomic number is the number of protons/ electrons in the neutral atom Mass number is the sum of # of protons + number of of neutrons Atomic weight is the weighted average of mass of all isotopes

The Quantum Numbers

Bohr's model of atom concluded that, electrons are restricted to certain energy levels sometimes called orbits or shells. Which n is the period the element is in. n=1,2,... This correspond to the Principal quantum # Later investigation shows that some of these energy elves have sub-levels. 1. in the first shell (n=1, L=0, and m_l=0), the electron occupy a region in space called s orbitals. An s orbital is identified by an angular momentum quantum #. For s orbital, L=0 - each atomic orbital can hold a max. of 2 electrons according to Pauli Exclusion Principle and no 2 electrons can have the same 4 quantum # 2. IN the second shell( n=2), the electrons can occupy 2 types of orbitals=s&p The atomic orbital can only hold 8 max. electrons 3.In the third shell(n=3), electrons can only occupy 3 types or orbitals: s,p,d the possible values of L=0,1,2 The max. electrons in orbitals =18 4. In the four shell(n=4), the electrons can occupy s, p, d, f. The orbitals can hold a max. of 32 electrons.

Contribution of Louie de Broglie to Atomic spectra and Bohr Atom(1925)

He said that very small particles such as electron, might also display wave properties under the proper circumstance. De Broglie equation: Wavelength/lambda=h(Planck constant)/m(mass).V(volume) Used to find wavelength when mass and volume are given.

What is the mass number?

Mass # is the sum of the number of protons plus(+) the # of neutrons

What are isotopes?

Isotopes are atoms of the same element but different masses/neutrons # Designating Isotopes: 12C6, 13C6, 14C6 They have the same # of protons/electrons but with different masses/neutrons #

How elements are arrange in the Periodic Table

Mendeleev listed the elements in order of increasing atomic weight with 3 exceptions where he had exchange elements in order to place them with the proper group

Are all the atoms of the same element identical?

No, because some are isotopes.

Contributions of Dmitri Mendeleev and Lothar Meyer Of P.T

The Periodic Table is arranged in increasing weight/ #proton -Vertical arrangement of similar properties and -The Horizontal groups are called ''periods'' -The Columns are called ''groups'' and have similar properties Physical and Chemical Properties of Metals/ non-metals Metals look shining and non-metal=not shining

The atomic number tells us what?

The atomic # tells us the # of proton in the the nucleus

How do you determine isotopes distribution in nature?

The instrument used is called a Mass Spectrometer, and is used to detect the # of particles. Separation depends on the mass particle.

The Electronic Structure of Atoms

We often study the light given off and absorbed by atoms to learn about how electrons are arranged in atoms

Atomic Spectra and the Bohr Atom

When atoms are excited, they often give off light. Ex: a rainbow spectrum. A continuous spectrum is when you can't tell where one color stops and another begins. Emission spectrum is a series of bright lines. How do you explain these spectra? a. spectrum produced by hydrogen consists of 4 lines in the visible region. b. J.R. Rydberg and J. Balmer found an equation that predicted these lines for hydrogen. 1/wavelength = R(1/n1^2- 1/n2^2), R=Rydberg constant=1.097E7m^-1 and n=the electron energy levels/integers that can be 1,2,3,... In 1913, Niels Bohr provided an explanation for this phenomena by presented the electron cloud. a.the nucleus of an atom is composed of neutron and proton. The closest the electron is to the nucleus, the lowest the energy. Electron traveled in an orbital around the nucleus. Electron must stay on track or energy levels, and if energy is supplied, electron goes to the next level. change in energy =hv, energy gaps are related to the frequency. Bohr claims that the n's levels in Rydberg(and Balmer) equation are # of orbitals. This means that as an electron is heated/has high energy, it will come from a lower energy level to a higher energy level. This is known as Absorption. Emission is when the electron comes from a higher energy level to a lower level as it give off heat or light. Ionization is the process when the electron goes from a lower energy level to infinity. Unfortunately, Bohr's model explained only hydrogen and other system with only 1 electron. He used classical mechanics of Newton. It does not work well for very small particles.