Structure of the Atom

J.J. Thompson (1903)

Cathode Ray Tube

Observations:

1. Speed of beam is ______________________________.

2. Beam deflected by _______________________.

3. Cathode rays can be produced______________________.

Conclusions:

1. Cathode rays are beams of _________________________________________.

2. All atoms contain ______________.

3. Atoms must contain _________________.

Thompson Model of the atom:

Ernest Rutherford (1911)

Rutherford wanted to test the Thomson Model by irradiating gold foil with a particles.

Conclusions:

1. Most of the mass of an atom must be located in _________________________________

2. The nucleus is made of ____________________________________.

3. The electrons move in a large volume which is mostly ___________________.

Rutherford Model:

Accounts for a particle scattering experiment, but not mass of atoms.

Rutherford-Chadwick Model (1932)

He atom:

1. Most of the atom's volume is occupied by ______________.

2. The number and arrangement of electrons in an atom determine its ____________________.

3. The identity of an element is determined by the no. of _______________ in the nucleus.

4. Different isotopes of elements exist and differ only in the no. of ___________ and hence the mass of the atom.

Symbol for isotope:

^A_ZX

A = mass no.

Z = atomic no.= no. of protons

X = symbol for element

isotopes of sodium:

²³₁₁Na ²⁴₁₁Na

atomic wgt of Na = 22.99 amu

Chemical Compounds

Molecular Compounds:

Properties:

1. solid, liquid, or gas; low melting pt. (why?)

2. insulators

3. high M.P. for covalent network solids

Ionic Compounds:

Properties:

1. Are usually solid with high melting points.

2. Form ions in water if cpd is soluble:

3. Do not conduct electricity in the solid state, but do so in the molten state and in aqueous solution. (why?)

4. Are usually brittle.