TXTBK: Elements of life Flashcards
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What are atoms made up of?
- subatomic particles
- protons
- neutrons
- electrons
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Describe the properties of a nucleus in an atom
- most of the mass of an atom = concentrated in the nucleus
- nucleus accounts for almost all mass but hardly any volume of an atom
- diameter of the nucleus = so small - compared to the whole atom
- most of the atom = empty space
- made up of
- protons + neutrons
- while electrons - move around nucleus
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Describe the properties of a proton
- relative mass = 1
- charge (relative to a neutron) = +1
- location in atom = in nucleus
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Why is relative mass and relative charge used to describe subatomic particles?
- Because mass and charge of subatomic particles = so small
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Describe the properties of a neutron
- relative mass = 1
- charge (relative to a neutron) = 0
- location in atom = in nucleus
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Describe the properties of an electron
- relative mass = 0.000549
- mass of an electron = negligible compared to mass of proton or neutron
- charge (relative to a neutron) = -1
- location in atom = around nucleus
- move around nucleus in shells
- these shells take up most of the volume of an atom
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What part of an atom takes part in chemical reactions?
- electrons in the outer parts of atoms interact together in chemical reactions
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What is the atomic number?
- atomic (proton) number may be described as Z
- number of protons in the nucleus of an atom
- numerically equal to the charge on the nucleus because neutrons have a neutral charge (0)
- all atoms of the same element have the same number of protons, doesnt change for different isotopes
- e.g. Z=6 for all carbon atoms (carbon-12, carbon-13 etc.)
mass number (A) = atomic number (Z) + number of neutrons (N)
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What is the mass number of an element?
- may be described as A
- mass number = number of protons and neutrons
- always has a whole number for its mass
- relative atomic mass - isn’t always a whole number but mass number is
mass number (A) = atomic number (Z) + number of neutrons (N)
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Label the following nuclear symbol
- Nuclear symbols identifies mass number, atomic number, and symbol of the element
- A = mass number
- Z = atomic (proton) number
- X = element symbol
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Fill in the table below
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How are ions different to atoms?
- Ions have different numbers of protons and electrons
- for (neutral) atoms (with no overall charge) the number of protons is the same as the number of electrons
- negative ions
- have more electrons than protons
- positive ions
- have less electrons than protons
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What are isotopes?
- Isotopes are atoms of the same element with the same atomic (proton) number but different numbers of electrons and as a result different mass numbers
- the atomic numbers are the same
- means same number of protons and electrons (if neutral)
- the atomic numbers are the same
- the number + arrangement of electrons decide the chemical properties of an element
- isotopes have the same configuration of electrons - so they have the same chemical properties
- isotopes of an element do have slightly different physical properties though
- e.g. different densities, rates of diffusion etc.
- this is because physical properties of an element often depend more on the mass of the atom
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Why is the atomic number sometimes left out, for example in 7Li?
- Don’t really need it
- because element’s symbol tells you the value of the atomic (proton) number
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What are the naturally occuring isotopes of chlorine and their abundances?
- 35Cl - 75%
- 37Cl - 25%
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What are the naturally occuring isotopes of iron and their abundances?
- 54Fe - 5.8%
- 56Fe - 91.7%
- 57Fe - 2.2%
- 58Fe - 0.3%
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What are the naturally occuring isotopes of bromine and their abundances?
- 79Br - 50%
- 81Br - 50%
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What are the naturally occuring isotopes of Calcium and their abundances?
- 40Ca - 96.9%
- 42Ca - 0.7%
- 43Ca - 0.1%
- 44Ca - 2.1%
- 48Ca - 0.2%
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What are the naturally occuring isotopes of Magnesium and their abundances?
- 24Mg - 79%
- 25Mg - 10%
- 26Mg - 11%
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What did the ancient Greeks believe was true about atoms?
- ancient Greeks thought that all matter was made from indivisible partices
- Greek word - atomos - means uncuttable
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What did John Dalyon describe atoms as?
- described atoms as solid spheres
- said that different spheres made up different elements
- as scientists did more experiments our currently accepted model began to emerge - with modifications and refinement being made to take account of new evidence
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Who disproved the idea that atoms were solid and indivisible?
- J J Thomson in 1897
- did a whole series of experiments and concluded that atoms were not solid and indivisible
- His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles
- he called these particles ‘corpuscles’ - now known as electrons
- The ‘solid sphere’ idea of atomic structure had to be changed
- new model was known as the ‘plum pudding model’ - a positively charged sphere with negative electrons embedded in it
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Describe the plum pudding model
- put forward by JJ Thomson in 1897 (discovered the electron)
- The ‘solid sphere’ idea of atomic structure had to be changed
- new model was known as the ‘plum pudding model’ - a positively charged sphere with negative electrons embedded in it
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Who disproved the ‘plum pudding model’?
- Ernest Rutherford and his students Hans Geiger and Ernest Marsden in 1909
- conducted the famous Geiger-Marsden experiment
- fired alpha particles (positively charged) at an extremely thin sheet of gold
- They expected, from the ‘plum pudding model’, that most of the alpha particles would be deflected very slightly by the positive ‘pudding’ that made up most of the atom
- because positive and positive charges repel
- however most of the alpha particles passed straight through the gold atoms, and only a few were deflected backwards
- plum pudding model - couldnt be right
- Rutherford came up with a new model that could explain this new evidence - the nuclear model of an atom
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Describe the nuclear model of the atom
- there is a tiny, postively charged nucleus at the centre of the atom, where most of the atom’s mass is concentrated
- The nucleus is surrounded by a ‘cloud’ of freely orbiting negative electrons
- Most of the atom is empty space
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What did Henry Moseley discover?
- discovered that charge of the nucleus increased from one element to another in units of one
- led Rutherford to investigate nucleus
- Rutherford discovered that it contained postively charged particles that he called protons
- the charges of the nuclei of different atoms could then be explained - atoms of different elements have a different number of protons in their nucleus
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Who discovered the neutron?
- there was a problem with Rutherfords model
- the nuclei of atoms were heavier than they would be if they just contained protons
- Rutherford predicted that there were other particles in the nucleus, that had mass but no charge
- neutron was eventually discovered by James Chadwick
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How normally does scientific knowledge develop?
- new evidence - prompts people to come up with new improved theories and ideas
- then other people go through each new, improved theory and try to find flaws and/or prove that they are true/correct
