Download Inside the Atom 1. Atom – greek for cannot be divided. Democritus

Inside the Atom
1. Atom – greek for cannot be divided. Democritus believed if you take a piece of matter and continue cutting it in
half eventually you wouldn’t be able to cut it anymore only one particle left = atom
2. Atom Models
a. In the 1800s, scientists discovered that all matter is made up of elements either in pure form Au, Ag or
Fe, or in combinations such as the molecules of H2O & NaCl
b. 1st Model: Dalton – proposed that the atom was a hard sphere which was the same all the way through.
Dalton’s idea of what atoms look like (marble)
c. 2nd Model: Thompson – discovered electrons in 1897 through experiments with gas particles and magnets –
he found that negatively charged particles were attracted to the positive pole of the magnet. Thompson’s
idea of the atom – with electrons sticking to the surface of the atom
d. 3rd Model: Rutherford – discovered that the extra mass in atoms comes from the neutrons in the nucleus.
He also discovered the nucleus also contains positively charged particles – protons. Rutherford’s idea of the
atom = nucleus inside and electrons outside (99% empty space)
e. 4th Model: Bohr – discovered how electrons were arranged around the nucleus electrons orbit around
the nucleus in calculated energy levels which helps scientists predict the likelihood of bonds between
different atoms
f.
5th Model: Electron Cloud Model – now we know that electrons orbit the nucleus in unpredictable paths –
but they still seem to be confined to energy levels as proposed by Bohr the electrons are attracted to
the positive protons in the nucleus but could bounce and move.
3. Periodic Table
a. Mendeleev in 1869 created the first periodic table which arranged the known elements at that time in
order of increasing atomic mass – each column or group contained elements with similar properties
i. he left blanks because he know more elements existed though they weren’t found yet
ii. later scientists did discover them => gallium, scandium and germanium
b. Moseby later found that the elements’ properties were more like its atomic number than atomic mass =>
he revised the table which revealed there were still missing elements (in order of increasing atomic
number)
c. 116 elements in all – 1 through 92 are naturally occurring and 93 – 116 are man-made or synthetic
d. On the table – there is a stair-step line which separates the metals from the non-metals (metals – to the
left of the line, non-metals to the right)
i. most elements are metals in the solid state at room temperature – Hg only liquid metal
4. Atoms
a. Everything is made of matter anything that has mass and takes up space (ex. air, food, water, etc.)
i. Light waves aren’t matter = contains no mass and doesn’t take up space
ii. All matter in the world looks different because of the types of atoms they contain
iii. Matter exists in 4 states gas, liquid, solid or plasma
iv. Matter has 2 properties physical & chemical
1. The properties of one type of matter differ from the properties of other matter because
matter is composed of atoms = the small particles that are the building blocks of matter
v. Inside the atom:
1. Protons – particles in the nucleus with a positive electrical charge
2. Neutrons – no electrical charge = neutral – found in the nucleus
a. the nucleus’ charge is overall positive == electrons balance them out
3. electrons – particles with a negative charge located outside the nucleus
vi. atomic number = number of protons in the atom and usually the same number of electrons
vii. ions -- all atoms are electrically neutral unless they gain or lose an electron through chemical
bonding (ex. NaCl – table salt) Na loses its last electron on the outermost energy level when it
bonds with Cl giving Na an overall positive charge = positive ion – the extra electron gained by Cl
through its bond with Na to form NaCl gives Cl an overall negative charge = negative ion
Radioactivity, Fission and Fusion
1. Radioactivity
a. Elements can have different numbers of neutrons in their nucleus
b. Atoms of the same element that have different numbers of neutrons = isotopes
c. The nucleus can become unstable if there are too many neutrons for the number of protons creating a
radioactive isotope
2. Radioactive isotopes
a. Give off radiation in the form of alpha, beta, and gamma particles
b. Gamma particles are high energy X-rays and can only be stopped by lead
c. All elements with atomic numbers greater than 83 are radioactive
d. When radioactive atoms emit alpha or beta particles and gamma rays they are going through radioactive
decay
i. Decay causes an atom of one element to transform into a different element by reducing its
atomic number
ii. Half-life = the time it takes for ½ of the particles in the nucleus of a radioactive atom to decay
(can take thousands – hundreds of thousands of years for radioactive elements to break down
into harmless or more common elements)
iii. Radiation affects the operation of living cells such as cancer or genetic defects small doses
are used in the diagnosis and treatment of diseases
Radioisotopes used in medicine
Isotopes
Half-life
Use
Arsenic – 74
17.9 days
Gold – 198
64.8 hours Test kidney activity
Barium – 131
11.6 days
Detect bone tumors
Iodine – 131
8.07 days
Treat thyroid problems
Radium – 225 14.8 days
Locate brain tumors
Treat skin cancer
Fission
Occurs when the nucleus of an atom with many protons and neutrons becomes so unstable it splits
into 2 smaller atoms releasing large amounts of energy fission reaction – can be used to create
heat in nuclear power plants through the use of nuclear reactors which control the reaction
Fusion
Also a nuclear reaction which occurs when the nucleus of 2 small atoms join or fuse together to
form 1 larger atom which releases energy
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Fusion reactions “power” the Sun – hydrogen atoms combine at extremely high
temperatures to form helium atoms