The Atom LOs Describe the structure and properties

The Atom LOs Describe the structure and properties of the atom Explain the history of atomic models

Nuclear symbol 12 C 6 Periodic table symbol 27 Al 13 Periodic table symbol 35. 5 Cl 17 24. 3 Mg 6

What is… 1) The atomic number of an element? 2) The mass number? 3) How do you establish the number of neutrons? 4) What is the relationship between protons and neutrons?

What can you say about this species? 2+ Mg

The subatomic particles Draw a table to show the properties of the protons, neutrons and electrons. Protons Neutrons Electrons

Let’s get back to magnesium 24 Mg 12 25 Mg 12 26 Mg What are these 3 called? How are the 3 atoms similar? How are the 3 atoms different? 12

Isotopes Atoms with the same number of protons, but a different number of neutrons. Same chemical properties, but WHY? Different physical properties, WHY?

Exam Questions

Atomic Models

Produce a flow diagram explaining how the model of the atom has evolved over time • Include the scientists name • How the model is better than the previous model • Evaluate how successful each model is (one sentence)

Group discussion

Plenary Can you explain atoms, their subatomic particles and their properties? Can you quickly calculate the number of protons neutrons and electrons in an atom from the nuclear symbol? Can you explain what an isotope is, and what this means for chemical and physical properties? Can you evaluate the different atomic models?

Starter: Linking and Synthesis How can you link Carbon-12 to the Bohr model of the nucleus? (3 marks)

Homework

What you should understand already 1) The 5 different models of the atom, and who proposed them 2) What you can work out from a nuclear symbol 3) What isotopes are, and what you can say about the chemical and physical properties

Relative isotopic mass Definition: The relative isotopic mass is the mass of an isotope of an element on a scale where an atom of carbon-12 is 12. u = unified atomic mass unit

Relative atomic mass Definition: The relative atomic mass (Ar) is the average mass of an atom of an element on a scale where an atom of carbon-12 is 12.

Relative molecular mass or Relative formula mass Definition: The relative molecular mass (Mr) is the average mass of a molecule or formula unit on a scale where an atom of carbon-12 is 12.

Relative Masses Why is the relative mass of magnesium 24. 3? Question) The relative abundance of atoms of magnesium are 84% 24 Mg, 2% 25 Mg and 14% 26 Mg. What is the relative atomic mass.

Relative Masses (2) Why is the relative mass of copper 63. 5?

Masses and Moles • Use p 10 and 11 to identify the key ideas you think are important. My ideas: Then we will discuss as a group and add or remove the key ideas: Group ideas:

Key equations

Exam Questions

Empirical Formula and Balancing equations

Plenary 1. Do you know the 3 definitions for the relative mass of atoms, isotopes and molecules. 2. Do you know what relative abundance means, and can you calculate the relative atomic mass in under 2 minutes? 3. Do you know what a mole is, what Avagadro’s constant is, and what links the relative mass and the mass of one mole.

Weighing Atoms It is very difficult to weigh individual atoms. Why?

Relative atomic masses To make life easier, scientists decided to compare masses against Carbon. We say carbon has a mass of 12, and elements are either lighter or heavier. This value is called the Relative Atomic Mass (Ar). For example: Hydrogen is much lighter than carbon: H (Ar) = 1 Mercury is much heavier than carbon: Hg (Ar) = 197

Relative Formula Mass The relative atomic mass is for each element in the periodic table. The relative formula mass is for compounds. Relative formula mass (Mr) E. g. Ca. CO 3 – Calcium Carbonate Mr = Ca + C + 3 x. O = 40 + 12 + (3 x 16) = 100

How do we know that… • Sodium Chloride is Na. Cl • Glucose is C 6 H 12 O 6 • Aluminium sulfate is Al 2(SO 4)3

Empirical formula This is a method to work out the simplest formula for compounds. You need to perform an experiment to work this out. If 10 g of calcium, reacts with 17. 8 g of chlorine, what is the empirical formula?

IN PAIRS – complete 1 each Question 1 9 g of aluminium reacts with 35. 5 g of chlorine. What is the empirical formula of aluminium chloride? Question 2 28 g of iron reacts with 16 g of oxygen. What is the empirical formula of iron oxide?

Alternative Question Compound Y is made up of only carbon, hydrogen, and oxygen atoms. The percentage composition is 59% carbon, and 33% oxygen. What is the empirical formula?

Empirical formula Use the empirical formula from the previous question. (also called the formula mass). Molecular formula The Mr of the compound is 200 g. What is the molecular formula? s

Empirical Formula Practical 1) Put a crucible and lid on a top pan balance, and record the mass. Mass (g) Crucible and lid 2) 3) 4) 5) Add 5 magnesium strips into the crucible, and record the mass again. Place the crucible on a clay triangle, and heat strongly with a Bunsen burner for 5 minutes. Put a heat proof mat on the top pan balance, and zero the balance. Place the hot crucible on the heat proof mat, and record the final mass. Crucible, lid and magnesium (before heating) Mass of magnesium Crucible, lid and magnesium (after heating) Mass of oxygen that reacted

Using your results Your results should look something like: Mass of magnesium = 0. 12 g Mass of oxygen = 0. 08 g Using the Ar(Mg) = 24 and Ar(O) = 16, calculate the formula. Empirical formula.

Moles…continued LOs 1) To be able to perform mole calculations with solid masses 2) To be able to perform mole calculations with solutions 3) To be able to perform mole calculations with gases

Atoms and moles 1) How many atoms are there in 2. 1 moles of lithium? 2) A sample contains 3. 4 x 1022. How many moles do you have?

Solids and moles 1) A sample contains 45. 7 g of ethanol (C 2 H 5 OH). How many moles do you have? 2) What is the mass of 0. 45 moles of magnesium?

Solutions and moles Concentration 1) What is the number of moles in 45 cm 3 of 0. 25 mol dm-3 solution? 2) What is the concentration of a solution, when 0. 34 moles of compound is dissolved in 500 cm 3 of water?

Gases and moles 1 mole of ANY gas has a volume of 24 dm 3 at room temperature and pressure (RTP). 1) How many moles of O 2 are present in 56 dm 3 at RTP? 2) What is the volume of 0. 46 moles of hydrogen gas at RTP?

Pulling triangles together

Standard Solutions 1) Decide on the concentration you need. 2) Check the volume on the flask. 3) Calculate the number of moles you need to make the concentration (conc triangle) 4) Calculate how many grams this is. 5) Add the sample to the flask 6) Fill to around 80% of the flask with distilled water. 7) Thoroughly mix by inverting. Then top up to the line.

Your turn Produce a 0. 25 mol dm-3 of sodium chloride.

Salts

Learning Objectives • Describe the reaction of an acid with carbonates, bases and alkalis to form a salt • Explain that salts are formed, when the H+ of an acid is replaced by the metal or NH+ • Explain that a base readily accepts H+ ions (examples include OH- and NH 3)

What is an acid? • Around 1810 Humphrey Davy discovered that hydrochloric acid is made of only hydrogen and chlorine • This led to it being established that hydrogen was common to all acids • An early definition of an acid states that they have at least one hydrogen atom that can be replaced by a metal atom + H

Bronsted-Lowry Theory • Stated that an acid is a proton donor and a base is a proton acceptor. • For example • HCl + NH 3 Cl- + NH 4+ • Note acids and bases can only react in pairs: one acid and one base

A salt is… • when the H+ of an acid is replaced by the metal • 1. Mg(s) + 2 HCl (aq) Mg. Cl 2(aq) + H 2(g) OR • when the H+ of an acid is replaced by the NH+ • Nitric Acid + Ammonium Hydroxide: • HNO 3 + NH 4 OH NH 4 NO 3 + H 2 O

Chemical reactions Hydrochloric acid (HCl) Sulphuric acid (H 2 SO 4) Citric acid (C 6 H 8 O 7) Magnesium oxide (Mg. O) Sodium Hydroxide (Na. OH)