Chemistry Atomic structure

Chapter 4, and Chapter 5, p. 146-148

Today’s summary

4.1, 4.2, 4.3, P. 146-148 Webquest on atomic emission spectra

4.1 history of the atom in thought

Early ideas about matter Democritus John Dalton

– Daltons atomic theory vs Democritus– Dalton = scientific method for experimental

evidence

4.1 conservation of mass

Mass, matter is not created or destroyed in ordinary chemical reactions

Nuclear reactions are a separate topic; NOT ordinary

4.2

Defining the Atom How we discovered the structure of the atom Who, which experiments

First

Electrons In CRTs, cathode ray tubes Stream of electrons was observed Sir William Crookes Mass and charge: J.J. Thompson Electromagnetic fields There is a particle smaller than an atom

Mass of electron

Thompson was able to determine the charge to mass ratio of the charged particle

Milikan calculated the mass of an electron Robert Milikan-oil drop experiment-

determined charge of an electron

The plum pudding (blueberry muffin model)

Created by JJ Thomson The model was a circle with electrons in a

disorganized pattern The model was changed to Rutherford’s

model

The nucleus

Rutherford– The Gold Foil Experiment

Protons and neutrons make up the dense center

Protons have positive charge Neutrons have negative charge Incredibly dense

Nucleus, slide 2

Positively charged nucleus react with positive alpha particles casing deflections

Electrons around the nucleus are negatively charged

Completing the model of the atom

Made of 3 subatomic – electron, proton, and neutron.

Atoms are shaped with small dense nucleus of positive charge surrounded by negative charge

Mostly consisted of fast moving electrons

4.3 how atoms differ

Atomic number Henry Moseiev discovered that atoms of

each element contain a unique positive charge in their nuclei

# of protons in an atom identifies it as an atom of a particular element.

# of protons= atomic # and # of electrons

Isotopes and mass number

Isotopes: atoms with the same # of protons but different #’s of neutrons

Mass of Isotopes: isotopes containing more neutrons have a greater mass

Isotope Notation: each isotope of an element is identified with a # called the mass #

Mass # = Atomic # + # of Neutrons

Mass of atoms

The atomic mass unit is what you measure the mass of an atom with

The atomic mass is the weighted average mass of the isotopes.

The atomic mass unit is one twelfth the mass of a carbon-12 atom.

The standard of atomic mass unit is Carbon-12, AMU is one-twelfth the mass of carbon atom

Atomic mass depends on the number of protons and neutrons

Atomic Emission Spectra

Electromagnetic Radiation- A form of energy exhibiting wavelike behavior as it travels through space (described by wave length, frequency, amplitude, and speed)

Electromagnetic Spectrum- Includes all forms of electromagnetic radiation

Atomic Emission Spectrum- A set of frequencies of electromagnetic waves given off by atoms of an element, consists of a series of fine lines of individual colors.

p. 146-148

When atoms have no added energy they are in their ground state.

When atoms acquire energy their electrons become exited and orbit at a further distance from the nucleus.

Bohr assigned each orbit a different value called a quantum number.

When the atom returns to its ground state the electrons revert to their closer orbits which release light energy that can be observed as the atomic emission spectrum.