Topic 1.1-1.12 - Atomic structure
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Describe Dalton’s model of an atom in 1803
-All substances are made of atoms. (He imagined these as tiny solid balls) Atoms are small particles that cannot be created, divided or destroyed. -Atoms of the same element are exactly alike, and atoms of different elements are different -Atoms join with other atoms to make new substances
How has the Dalton model changed over time as a result of the discovery of subatomic particles?
-In 1897 J.J. Thomson discovered negative electrons -In 1909 Rutherford discovered that atoms have a nucleus with electrons around it. We now know that: ﹒Atoms can be broken down into 3 smaller particles: protons, neutrons and electrons ﹒Atoms of an element have identical numbers of protons and electrons, but can have different numbers of neutrons ﹒Atoms of different elements have different numbers of protons and electrons
Explain why atoms contain equal numbers of protons and electrons
Atoms are neutral and the charges on a proton are +1 and on an electron are -1 so the amount of protons = amount of electrons to cancel out and make the atom neutral
Describe the structure of an atom
A nucleus containing protons and neutrons, surrounded by electrons in shells
What is the meaning of the term ‘mass number’ of an atom?
Mass number = number of protons + neutrons
What are the relative charges and masses of protons, neutrons and electrons?
Proton’s charge: +1 Neutron’s charge: 0 Electron’s charge: -1 Proton’s mass: 1 Neutron’s mass: 1 Electron’s mass: 1/1836
Describe the mass of an atom
Most of the mass of an atom is concentrated in the nucleus
Describe the size of an atom’s nucleus
The nucleus of an atom is very small compared to the overall size of an atom
Describe the number of protons in an atom of an element relatively
An atom has the same number of protons in the nucleus, this number is unique to that element
Describe isotopes
Different atoms of the same element containing the same number of protons but different number of neutrons in their nuclei.
How do you calculate the number of protons, neutrons and electrons in atoms based on the periodic table?
The atomic number = the number of protons = the number of electrons. The mass number - atomic number = the number of neutrons
Explain how the existence of isotopes results in relative atomic masses of some elements not being whole numbers
-Because isotopes have the same number of protons but different numbers of neutrons, they are still atoms of the same element but have different atomic masses, because mass is calculated based on the mass of the neutrons and protons as mass is concentrated in the nucleus -The relative atomic mass (R.A.M/Ar) is calculated using the abundance of different isotopes and because it is an average it can lead to the RAM not being a whole number
How would you calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes?
R.A.M = (mass of isotope-A x % of isotope-A) + (mass of isotope-B x % of isotope-B) ÷ 100