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Topic 1 – Atomic Structure and the Periodic Table Revision Checklist SubtopicClass NotesRevision NotesPast Exam Questions C2.1 Mendeleev C2.2 Structure.

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Presentation on theme: "Topic 1 – Atomic Structure and the Periodic Table Revision Checklist SubtopicClass NotesRevision NotesPast Exam Questions C2.1 Mendeleev C2.2 Structure."— Presentation transcript:

1 Topic 1 – Atomic Structure and the Periodic Table Revision Checklist SubtopicClass NotesRevision NotesPast Exam Questions C2.1 Mendeleev C2.2 Structure of an atom C2.3 The modern periodic table C2.4 Electron shells

2 The history of the periodic table 1798: Lavoisier began to divide the elements into metals and non-metals. 1860: 63 elements were known. John Newlands noticed that when the elements were put in order of atomic mass, that every eighth element had similar properties. But this only worked as far as calcium C2.1 Mendeleev

3 1871: Mendeleev Mendeleev arranged the elements in order of atomic mass He arranged the elements so that elements with similar properties were in the same vertical columns (groups). He thought there must still be some elements to discover so left gaps for them. He used the gaps to predict the properties of the undiscovered elements. For example he predicted the properties of Eka Aluminium (what we now know as Gallium) C2.1 Mendeleev

4 Elements Definition…Element: A element is made up of only one type one atom. It cannot be spilt into simpler substances These atoms are ALL iron – theres nothing else in here C2.2 Structure of an atom

5 Ideas about atomic structure have changed over time. In 1803, John Dalton said atoms were solid spheres of matter that could not be split. Dalton also suggested that each element contained identical atoms. Atomic Structure C2.2 Structure of an atom

6 In 1897, whilst studying cathode rays, JJ Thomson discovered tiny particles with a negative charge. His discovery did not fit with Daltons model of the atom. Ernest Rutherford suggested that an atom is mostly empty space with its positive charge and most of its mass in a tiny central nucleus. Electrons orbited this nucleus at a distance, like planets around the Sun. nucleus electrons C2.2 Structure of an atom

7 nucleus neutron proton electron Atomic Structure C2.2 Structure of an atom

8 There are two properties of subatomic particles that are especially important: 1. Mass 2. Electrical charge The atoms of an element contain equal numbers of protons and electrons and so have no overall charge almost 0 C2.2 Structure of an atom

9 How many protons? The atoms of any particular element always contain the same number of protons. For example: The number of protons in an atom is known as its atomic number or proton number. It is the smaller of the two numbers shown in most periodic tables. hydrogen atoms always contain 1 proton; carbon atoms always contain 6 protons; magnesium atoms always contain 12 protons, C2.3 The modern periodic table

10 Mass number Electrons have a mass of almost zero, which means that the mass of each atom results almost entirely from the number of protons and neutrons in the nucleus. The sum of the protons and neutrons in an atoms nucleus is the mass number. It is the larger of the two numbers shown in most periodic tables C2.3 The modern periodic table

11 The actual mass of a hydrogen atom is 1.7x g (thats g!) Far too small a number to easily get your head around… So – we use Relative Atomic Mass instead (A r ) Relative Atomic Mass We compare the mass of each element to carbon-12 Carbon 12 has 6 protons and 6 neutrons so we say its A r = 12 Magnesium has the same mass as 2 carbon atoms so we say its A r = 24 C2.3 The modern periodic table

12 Why does chlorine have an A r of 35.5? …because there are different isotopes of chlorine C2.3 The modern periodic table

13 …have the same number of protons and electrons, but different numbers of neutrons. E.g. hydrogen has 3 isotopes… H 1 1 H 2 1 H 3 1 HydrogenDeuteriumTritium Isotopes Isotopes always have the same atomic number, but different mass number C2.3 The modern periodic table

14 Chlorine always has 17 protons, but some have 18 neutrons, others have 20 neutrons Isotopes The relative abundance (proportion) of Chlorine-35 is 75% The relative abundance (proportion) of Chlorine-37 is 25% We can use the A r and relative abundance of the isotopes to work out the A r of the element. C2.3 The modern periodic table

15 Example: Isotopes The relative abundance (proportion) of Chlorine-35 is 75% The relative abundance (proportion) of Chlorine-37 is 25% Q1: Calculate the A r of Neon C2.3 The modern periodic table

16 Q1: Calculate the A r of Neon Q2: Calculate the A r of Lithium Q3: Calculate the A r of Iron Q4: Calculate the A r of Silicon Q5: Calculate the A r of Mercury The table shows the natural relative abundance of the main isotopes of mercury, Hg. Mass number % Relative abundance C2.3 The modern periodic table

17 The Modern Periodic Table Elements are arranged in order or increasing atomic number (number of protons) Horizontal rows are called periods Vertical rows are called groups (the period number tells you the number of electron shells) Elements in the same group have similar properties (because they have the same number of outer electrons) Most elements are metals (in yellow on the left), non-metals are shaded in blue C2.3 The modern periodic table

18 Electrons are held in shells The first shell can hold upto 2 electrons The second shell can hold upto 8 electrons The third shell can hold upto 8 electrons Electronic Structure No. of electrons in 1 st shell No. of electrons in 2 nd shell No. of electrons in 3 rd hell C2.4 Electron shells


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