Science (Semester 1) Flashcards
What are atoms made up of?
Matter
Draw a diagram of an atom.
CARBON ATOM: 6 protons + 6 neutrons in nucleus 6 electrons spread across two rings 2 in first ring 4 in second
What is a scientific theory?
a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation
How can theories be revised?
Theories are revised gradually as scientists find improvements to the theory and ‘build’ upon it.
How can theories be disproved?
Theories can be disproved by experimental results contrary to a theory’s predictions.
Discuss the atomic theory proposed by Dalton.
Dalton’s atomic theory was based on experimentation and first-hand examination. This made his theory the first scientific theory.
Summarise Dalton’s atomic theory of matter
- All matter is composed of atoms, which are indivisible and indestructible
- All atoms of an element are identical, but different elements have atoms of differing size and mass
- All compounds are formed by combinations of atoms in defined ratios.
- Chemical reactions result in the rearrangement of atoms in the reactant and product compounds
Recall some of the early models of the atom.
- Democritus’s atomic theory
- Dalton’s atomic theory of matter
- Thomson’s plum pudding model
- Rutherford model
Discuss Thomson’s Plum Pudding model of the atom.
- Atom composed of electrons
- Electrons surrounded by a ‘soup’ of positive charge to balance electron’s negative charge
- Electron arranged in rotating rings
Describe Rutherford’s gold foil experiment.
- Alpha particles with large kineticenergies were shot towards a thin foil of gold
- A ‘ring’ detector was set up around the gold foil to detect the alpha particles and where they scattered
- Most of the alpha particles passed through, but others were deflected at small angles or REFLECTED BACK AT THE SOURCE.
- This indicated a strong central positive charge.
Describe the gold foil experiment’s implications for the structure of the atom.
- Disproved Plum Pudding model
- Revealed that atom was mostly empty space
- Strong central positive charge in nucleus, which has majority of mass
- Electrons moved around in space around nucleus
- Thus, new planetary model was developed.
Discuss Rutherford’s gold foil experimental setup.
- A radioactive source rich in positively charged heavy alpha particles was inside a cube shaped thick lead box with a narrow opening
- The narrow opening confined the alpha particles into a beam
- A thin gold foil was set up away from the radioactive source (which would be bombarded by the alpha particles)
- A circular florescent detector was set up around the gold foil - screen coated with zinc sulphide flashed when alpha particles hit it
How were the results of the gold foil experiment interpreted?
- Most of the alpha particles passed through the foil undeflected: Atom mostly empty space
- Some alpha particles deflect by small angles: Strong positive charge in nucleus
- Small fraction of alpha particles reflected back: Nucleus has most of mass
Why did Rutherford propose the existence of neutrons?
- Atomic number of atom usually above half its atomic mass
- However, nuclei with 2x charge had at least double the mass that was expected from the protons contained (DISPARITY)
Why was it difficult for Rutherford to prove the existence of neutrons?
Neutrons hold no charge, thus they could not be detected by electric/magnetic fields.
What charge does a proton hold?
Positive
What charge does an electron hold?
Negative
What charge does a neutron hold?
None
Calculate the numbers of protons, neutrons and electrons in an atom given its mass and atomic numbers.
Atomic number = no. of protons = no. of electrons
Mass number = no. of protons + no. of neutrons
Neutrons = atomic number - mass number
Explain the relative atomic mass scale.
weighted average of masses of isotopes in a naturally occurring element relative to mass of carbon-12 atom (standard)
How are atomic numbers determined?
Atomic number = no. of protons = no. of electrons
How are mass numbers determined?
Mass number = no. of protons + no. of neutrons
What are isotopes?
different forms of an atom that vary in mass and number of neutrons
How are isotopes similar and different?
- Isotopes (of the same element) share similar physical/chemical properties
- Isotopes differ in their number of neutrons and thus atomic mass
- Some isotopes are unstable, and will undergo radioactive decay to become another element.