Atoms and Elements Flashcards
Which figures are significant?
1) All non-zero digits (Eg: 1.234 g)
2) Zeroes between non-zeros (Eg: 1002 mL)
3) Trailing zeros that are to the right of a decimal point but only if they are in between non-zeros (Eg: 0.2030 mL)
Which figures are insignificant?
1) Leading zeros (zeros to left of first nonzero digits) bc they only serve to indicate the position of the decimal point. (Eg: 0.001°C)
2) When a number ends in zeroes but there isn’t a decimal point (Eg: 1340 g)
How many significant figures should you put in a scientific calculation?
the amount in the (starting) number with the least significant figures
List the first atomic theory (Dalton)
1) All Matter is composed of tiny indivisible particles called atoms.
2) All atoms of the same element are identical.
3) Different elements are composed of different size atoms with their own properties such as mass.
4) Atoms of different elements combine in small whole number ratios to make up the molecule of a
compound.
5. New substances are created during chem reactions but law of conservation of mass
What did Aristotle believe about matter?
➣ matter consists of one continuous ribbon that you can’t pick apart (like sand).
➣ matter is infinitely divisible (you could keep cutting it but it would never stop).
What did Democritus believe about matter?
➣ matter consists of solid, separate, indivisible particles.
➣ These particles are all identical to one another.
Describe Thompson’s atomic experiment
Thompson took an evacuated glass tube and connected it to electricity. He noticed that there was a beam of
electricity that went right through the tube (cathode ray).
Thompson realized that because the beam travelled in a
straight line, it must have been made up of either particles or light. When he inserted a propeller into the tube, it spun. Therefore, the beam was made up of particles bc their mass made it spin.
Thompson then placed 2 metal plates outside the tube.
One was positively charged, and the other was negatively
charged. He noticed that the beam bent towards the
positive plate. This meant that it had a negative charge bc
opposites attract. Thompson concluded that atoms are
divisible. He called the particles that made up the beam
electrons.
Thomson also discovered that cathode rays are
identical regardless of the metal used to create the
cathode. Thompson therefore concluded that all atoms
contain electrons.
What are the properties of alpha particles?
1) positive charge
2) Travel in straight lines
3) Weak penetrating power
4) Have a mass
5) Move at a moderate speed
What are the properties of beta particles?
1) Negative charge
2) Travel in straight lines
3) Stronger penetrating power
4) Small mass
5) Fast moving
What are the properties of gamma rays?
1) Neutral charge
2) travel in straight lines
3) Extreme penetrating power
4) Fast moving
5) high energy
Symbol for alpha particles
α
Symbol for beta particles
β
Symbol for gamma rays
ϒ
Describe Rutherford’s model of the atom
The atom is electrically neutral (same # of protons and
electrons). It has a dense positive center called the nucleus. Electrons orbit the nucleus, leaving a large space between it and them
What did Rutherford predict about his experiment?
only a few alphas would be deflected slightly from contact w an electron. the rest would pass through the gold foil.
