Atomic Structure Flashcards
(38 cards)
Define an atom
Smallest particle of an chemical element that can exist.
Define atomic number (Z)
The number of protons in the nucleus of an atom.
Define mass number (A)
The total number of protons and neutrons in a nucleus.
Define Relative Atomic Mass (Ar) using the C12 scale
It is the average of the mass numbers of isotopes of the element, as they occur naturally taking their abundances into account, relative to 1/12th mass carbon 12 atom.
Define an isotope
Atoms of the same element with the same number of protons but different number of neutrons.
What is the law of conservation of mass?
The law of conservation of mass is that matter cannot be created or destroyed. It can change forms but is conserved.
What particles make up everything?
Atoms, Ions and Molecules
Can atoms be created or destroyed?
Atoms cannot be created or destroyed.
What do the Greeks contribute to chemistry?
They said that all matter is made up of very small particles.
What did Dalton contribute to chemistry?
He said that atoms are indivisible and cannot be broken down any further.
What are cathode rays?
Streams of negatively charged particles called electrons which travel in straight lines.
What did Crooks Do?
He passed an electric current through an electric tube.
What did Crooks discover?
He noticed that there was radiation was coming from the negative electrode.
What did Crooks call the radiation?
He called the rays of radiation cathode rays.
What did Stoney contribute to chemistry?
He suggested naming the particles found in cathode rays ‘electrons’.
What was J.J. Thompson’s primary experiment in the development of atomic theory?
- He passed cathode rays through a small hole in the anode to get a narrow beam, the spot where it hit the glass fluoresced.
- when there was no charge the beam remained straight, but when positive and negative charges were added the beams moved towards the positive plate.
- Thompson concluded that the rays must be negative due to it moving towards the positive plate.
What was J.J. Thompson’s secondary experiment in the development of atomic theory?
- This time he applied a magnetic tube outside the glass tube, he found that electrons were also deflected by a magnetic field and adjusted the strength so that the means would go straight.
- From the result of the experiment he was able to calculate the ratio of the charge of the electron (how negative it is) to the mass of the electron. The ratio is simply given as e/m.
What is the formula for the charge of an electron
E/M= -1.76x10^8
What was Millikans experiment?
He used charged plate to measure the charge of an electron.
What did Millikan’s experiment find?
Using Thompson’s charge to mass ratio (e/m), the mass of the electron was found.
What did Rutherford discover?
Rutherford discovered the nucleus and proton.
What was Rutherford’s experiment?
- He shot alpha particles at a sheet of gold foil. Alpha particles are positively charged particles. He expected oil particles to pass straight through with slight deflections due to protons and neutrons.
- Most of the alpha particles passed through. Meaning, most of the atom must be made of empty space. He concluded that there must be a dense core of positive charge within the atom. The small dense core was called the nucleus of the atom.
How did Chadwick discover the neutron?
He found a beam of particles that weren’t deflected by magnetic or electric fields. Since the particles had no charge they care called neutrons.
How did Neils Bohr adapt the nuclear model?
- He concluded that the different arrangments of electrons in each atom must explain why each element had different emission line spectrums.
- He concluded that electrons revolve around the nucleus in fixed paths called energy levels and that each energy level has a fixed amount of energy.
