Atomic structure Flashcards
Key concepts in chemistry
abundance
Definition
If there is a lot of something, it is described as being abundant.
atom
Definition
The smallest part of an element that can exist.
atomic number
Definition
The number of protons in the nucleus of an atom. Also called the proton number.
charge (electrical)
Definition
An imbalance of electrons and protons in a material. An excess of electrons results in negative charge, a deficit of electrons results in positive charge.
electron
Definition
Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.
element
Definition
A substance made of one type of atom only.
isotope
Definition
Atoms of an element with the same number of protons and electrons but different numbers of neutrons.
mass
Definition
The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g).
mass number
Definition
The number of protons and neutrons found in the nucleus of an atom.
neutral atom
Definition
An atom in which the number of protons and electrons is the same.
neutron
Definition
Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.
nuclei
Definition
Nuclei is the plural of nucleus. The nucleus is the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom.
nucleus
Definition
The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei.
particle
Definition
A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules.
properties
Definition
The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point.
proton
Definition
Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1.
relative atomic mass
Definition
The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.
relative mass
Definition
The relative mass is the number of times heavier a particle is, compared to another.
subatomic particle
Definition
Objects found in atoms, including protons, neutrons and electrons.
What is Dalton’s model
overview
John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny solid balls.
Dalton’s model included these ideas:
atoms cannot be broken down into anything simpler
the atoms of a given element are identical to each other
the atoms of different elements are different from one another
during chemical reactions atoms rearrange to make different substances
Dalton’s model has changed over time due to what?
The Dalton model has changed over time because of the discovery of subatomic particles.
What was discovered in 1897?
Electrons
What was discovered in 1909 -1911?
Atoms have a nucleus with electrons around it
What was discovered in 1913
Electrons occupy shells (energy levels)
What was discovered in 1918?
Protons
What was discovered in 1932?
Neutrons
As a result of the discoveries of: Electrons; Atoms having a nucleus with electron around it; Electrons occupy shells (energy levels); Protons; Neutrons, we know know what?
atoms can be broken down into three 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
Atoms can be broken down into what?
atoms can be broken down into three smaller particles: protons, neutrons and electrons
Atoms of an element
Number of protons, electrons and neutrons
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 what?
atoms of different elements have different numbers of protons and electrons
The nucleus is very small compared to the atom as a whole:
the diameter of a nucleus can be 100,000 times less than the diameter of an atom
as electrons are even smaller, most of an atom is empty space
What do the nuclei of all atoms contain?
The nuclei of all atoms contain subatomic particles called protons and most also contain neutrons.
Masses of subatomic particles
The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
The mass of electrons is very small compared to protons and neutrons. Since a nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.
Mass of an atom
Since a nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.
Comparative charges of protons and electrons
Protons and electrons have opposite electrical charges.
Relative mass of a proton?
1
Relative mass of a neutron?
1
Relative mass of an electron?
1 ÷ 1835
Relative charge of a proton?
+1
Relative charge of a neutron?
0
Relative charge of an electron?
-1
Which subatomic particles are positive, negative or neutral?
Protons are positive
Neutrons are neutral
Electrons are negative
What is the number of protons in the nucleus of an atom called?
The Atomic number
Atomic number of all the atoms of a given element is?
all the atoms of a given element have the same atomic number
Atomic numbers of different elements
the atomic number of each element is unique - no two elements have the same atomic number
Link between number of electrons and protons in any atom
An atom contains equal numbers of protons and electrons.
Since protons and electrons have equal and opposite charges, this means that atoms are neutral overall.
Overall charge of any atom
Neutral.
because all atoms have the same number of protons (positively charged) and neutrons (negatively charged)
What is the total number of protons and neutrons in an atoms nucleus called?
The mass number
on the periodic table, the which numbers are the mass number and which are the relative atomic mass?
Number at the top = Mass number
Number on the bottom = Relative atomic mass
To calculate the numbers of subatomic particles in an atom use its atomic number and mass number:
number of protons = atomic number
number of electrons = atomic number
number of neutrons = mass number - atomic number
Q. The atomic number of a chlorine atom is 17 and its mass number is 35. Calculate the number of protons, neutrons and electrons it contains.
Number of protons = 17
Number of electrons = 17
Number of neutrons = (35-17)=18
Atoms of an element that have the same number of protons, but different numbers of neutrons in their nuclei are called what?
Isotopes
Isotopes of an element have:
- the same atomic number
- different mass numbers
All hydrogen atoms contain how many types of protons, neutrons and electrons?
All hydrogen atoms contain one proton (and one electron), but they can contain different numbers of neutrons.
What is the most abundant isotope of hydrogen?
Hydrogen-1
How many protons, neutrons and electrons does the isotope Hydrogen-1 have?
Protons: 1
Neutrons: 1 - 1 = 0
Electrons: 1
How many protons, neutrons and electrons does the isotope Hydrogen-2 have?
Protons: 1
Neutrons: 2 -1 = 1
Electrons: 1
How many protons, neutrons and electrons does the isotope Hydrogen-3 have?
Protons: 1
Neutrons: 3 - 1 = 2
Electrons: 1
What is an isotope named after?
An isotope is named after the element and the mass number of its atoms. For example, carbon-12 is an isotope of carbon with a mass number of 12.
Chemicals properties of all three isotopes of hydrogen
All three isotopes of hydrogen have identical chemical properties. This is because the number of electrons determines chemical properties, and all three isotopes have one electron in their atoms.
What is the weighted average of the relative atomic masses of the isotopes in the element celled?
The relative atomic mass of an element
What is the relative atomic mass of an element?
The relative atomic mass of an element is the weighted average of the relative atomic masses of the isotopes in the element.
What symbol do relative atomic masses have?
Relative atomic masses are given in the periodic table. They have the symbol Ar.
Take care not to confuse mass numbers and relative atomic masses:
mass numbers are always whole numbers (it is not possible to have part of a proton or neutron)
relative atomic masses are often rounded to the nearest whole number, but are actually not whole numbers
Why is the relative atomic mass of chlorine not a whole number?
Chlorine naturally exists as two isotopes, (chlorine-35) and (chlorine-37). The abundance of chlorine-35 is 75% and the abundance of chlorine-37 is 25%. In other words, in every 100 chlorine atoms, 75 atoms have a mass number of 35, and 25 atoms have a mass number of 37.
The relative atomic mass, Ar, of an element is calculated from:
the mass numbers of its isotopes
the abundance of these isotopes
Calculate the atomic mass, Ar of chlorine.
25% of chlorine is isotope: chlorine-37
75% of chlorine is isotope: chlorine-35
Ar = ((35 x 75) + (37 x 25)) ÷ (75 + 25)
Ar = (2625 + 925) ÷ 100
= 3550 ÷ 100
Ar = 35.5 (to 1 decimal place)
Equation for relative atomic mass
Ar = total mass of atoms ÷ total number of atoms
Q. Calculate the relative atomic mass of copper. Give your answer to 1 decimal place.
69% of copper is copper-63
31% of copper is copper-65
Ar = ((63 x 69) + (65 x 31)) ÷ (69 +31)
Ar = (4347 +2015) ÷ 100
= 6362 ÷ 100
Ar = 63.6
Which of Dalton’s ideas about atoms is no longer thought to be true?
Atoms cannot be broken down into anything simpler
What makes up the nucleus of most atoms?
Protons and neutrons
Which of the subatomic particles has a mass of almost zero?
Electrons
Why are most atoms neutral?
Because they have equal numbers of protons and electrons
How many protons, neutrons and electrons are in an atom which has an atomic number of 11 and a mass number of 23?
11 protons, 12 neutrons, 11 electrons
What is the atomic number and the mass number of an atom with 29 protons, 36 neutrons and 29 electrons?
Atomic number = 29, Mass number = 65
What is the name for atoms with the same atomic number but different mass numbers?
isotopes
Boron naturally exists as two isotopes, boron-10 and boron-11. The abundance of boron-10 is 20% and the abundance of boron-11 is 80%. Using these figures, what is the relative atomic mass of boron?
10.8
