Atoms the building blocks All substances are made

Atoms – the building blocks • All substances are made from very tiny particles called atoms. • John Dalton had ideas about the existence of atoms about 200 years ago but only recently have special microscopes been invented that can “see” them. Water © Boardworks Ltd 2003

Elements – different types of atom • Elements are the simplest substances. There about 100 different elements. Two of John Daltons ideas were: – Elements contain different types of atom. – Each element has only one type of atom. O S N Fe K C © Boardworks Ltd 2003

Atoms – How Small? N • Atoms are about 1/100, 000 cm across. They are small. X 3, 000, 000 • To make an atom the size of a football we would have to magnify it to around 3, 000, 000 times its normal size • If we magnified the size of a football by the same amount it would stretch from the UK to the USA! © Boardworks Ltd 2003

Even Smaller Particles! • For some time people thought atoms were the smallest particles and that they could not be broken into anything smaller. • We now know that atoms are themselves made from even smaller and simpler particles. • These particles are – Protons – Neutrons – Electrons © Boardworks Ltd 2003

How Are the Particles Arranged? • Protons, neutrons and electrons are NOT evenly distributed in atoms. • The protons and neutrons exist in a dense core called the nucleus. • Around the outside are very thinly spread electrons. • These electrons exist in layers called shells. The Nucleus a dense core of protons and neutrons containing nearly all the mass of the atom ‘Shells’ of electrons are really very tiny so the atom is mostly empty space. © Boardworks Ltd 2003

Properties of Sub-atomic Particles • There are two properties of sub-atomic particles that are especially important: – Mass – Electrical charge Particle Protons Neutrons Electrons Charge Relative Mass +1 1 0 1 -1 0. 0005 Element atoms contain equal numbers of protons and electrons and so have no overall charge © Boardworks Ltd 2003

Atomic Number • The atom of any particular element always contains the same number of protons. E. g. – Hydrogen atoms always contain 1 proton – Carbon atoms always contain 6 protons – Magnesium atoms always contain 12 protons 12 • The number of protons in an atom is known as its atomic number. • It is the smaller of two numbers shown in most periodic tables C 6 © Boardworks Ltd 2003

How Many Protons? • Note that any element has a definite and fixed number of protons. • If we change the number of protons in an atom then this changes that atom into a different element. • Changes in the number of particles in the nucleus (protons or neutrons) is very rare It only takes place in nuclear processes such as radioactive decay, nuclear bombs or nuclear reactors. © Boardworks Ltd 2003

Mass Number • The mass of each atom results almost entirely from the number of protons and neutrons that are present. (Remember that electrons have a relatively tiny mass). • The sum of the number of protons and neutrons in an atom is the mass number Atom Protons Neutrons Mass Number Hydrogen 1 0 1 Lithium 3 4 7 Aluminium 13 14 27 © Boardworks Ltd 2003

How Many Neutrons 2 • It is not strictly true to say that elements consist of one type of atom. • Whilst atoms of a given element always have the same number of protons, they may have different numbers of neutrons. • Atoms that differ in this way are called isotopes. Remember: The number of protons defines the element © Boardworks Ltd 2003

How Many Neutrons 3 • Isotopes are virtually identical in their chemical reactions. (There may be slight differences in speeds of reaction). • This is because they have the same number of protons and the same number of electrons. • The uncharged neutrons make no difference to chemical properties but do affect physical properties such as melting point and density. © Boardworks Ltd 2003

Isotopes: Carbon • Natural samples of elements are often a mixture of isotopes. About 1% of natural carbon is carbon-13. 12 6 C 99% 6 6 6 1% Protons Electrons Neutrons 13 6 C 6 6 7 © Boardworks Ltd 2003

Isotopes: Hydrogen • Hydrogen exists as 3 isotopes although Hydrogen-1 makes up the vast majority of the naturally occurring element. 1 1 H Protons Electrons Neutrons Hydrogen 2 1 H Protons Electrons Neutrons (Deuterium) 3 1 H Protons Electrons Neutrons (Tritium) © Boardworks Ltd 2003

Isotopes: Chlorine • About 75% of natural chlorine is 35 Cl the rest is 37 Cl. 37 35 Cl 17 Protons Electrons Neutrons 17 17 18 75% 25% Protons Electrons Neutrons Cl 17 17 17 20 © Boardworks Ltd 2003

Activity Isotopes of Oxygen 16 • Almost all of natural oxygen is but about 0. 2% is 18 O. • Produce a Table showing the particles in each isotope. 16 O Oxygen-16 O 8 Oxygen-18 Protons 8 Electrons 8 Neutrons 10 © Boardworks Ltd 2003

Isotopes and Relative Atomic Mass • Many natural elements are a mixture of isotopes. • This means that when we react atoms of an element we are using a mixture of atoms with different mass numbers. • The relative atomic mass given in the periodic table takes account of this. E. g. . For 100 atoms of chlorine: Mass of 75 atoms of Chlorine 35: 75 x 35 =2625 Mass of 25 atoms of Chlorine 37: 25 x 37 =925 Total = 3550 Average (divide by 100) = 35. 5 © Boardworks Ltd 2003

Activity Drag the statements at the top onto the correct side of the table © Boardworks Ltd 2003

Summary: The atom so far! The nucleus. • Dense: contains nearly all the mass of the atom in a tiny space. • Made up of protons and neutrons. • Has a positive charge because of the protons. The electrons. • Exist thinly spread around the outside of the atom. • Very small and light. • Negatively charged. • Exist in layers called shells. • Can be lost or gained in chemical reactions. © Boardworks Ltd 2003

How Are Electrons Arranged? • Electrons are not evenly spread. • The exist in layers known as shells. • The arrangement of electrons in these shells is often called the electron configuration. 1 st Shell 2 nd Shell 3 rd Shell 4 th Shell © Boardworks Ltd 2003

How Many Electrons per Shell? • Each shell has a maximum number of electrons that it can hold. The maximum 1 st Shell: 2 electrons 2 nd Shell: 8 electrons 3 rd Shell: 8 electrons © Boardworks Ltd 2003

Which Shells Do Electrons go into? • Opposites attract. • Protons are + and electrons are – charged. • Electrons will occupy the shells nearest the nucleus unless these shells are already full. 1 st Shell: Fills this first 2 nd Shell: Fill this next 3 rd Shell: And so on © Boardworks Ltd 2003

Working Out Electron Arrangements 1. How many electrons do the element atoms have? (This will equal the atomic number). 2. Keeping track of the total used, feed them into the shells working outwards until you have used them all up. Drawing neat diagrams helps you keep track! 1 st Shell: Fills this first 2 nd Shell: Fill this next © Boardworks Ltd 2003

The Electrons in Carbon © Boardworks Ltd 2003

The Electrons in Neon © Boardworks Ltd 2003

The Electrons in Silicon © Boardworks Ltd 2003

Electrons in Phosphorus © Boardworks Ltd 2003

The Electrons in Argon © Boardworks Ltd 2003

The Electrons in Sodium © Boardworks Ltd 2003

The Electrons in Fluorine © Boardworks Ltd 2003

The Electrons in Aluminium © Boardworks Ltd 2003

The Electrons in Nitrogen © Boardworks Ltd 2003

The Electrons in Sulfur © Boardworks Ltd 2003

The Electrons in Oxygen © Boardworks Ltd 2003

The Electrons in Chlorine © Boardworks Ltd 2003

The Electrons in Magnesium © Boardworks Ltd 2003

Ions and Electron Structures 1. Ions are atoms that have either extra electrons added or electrons removed. e. g. Atoms Protons Electrons Lose 1 electron 1+ ion Gain 1 electron Protons Electrons So in ions the number of electrons no longer equals the number 1 - ion Protons Electrons of protons © Boardworks Ltd 2003

Positive Ions • These are ions formed by the atom losing one or more electrons. Lost 1 e- • • • + They are called cations This is because during It is nearly they move towards the cathode. electrolysis (Or Ions usually always they are Lost because “pussytive”!). have 2 e 2+ metal OUTER atoms that on the ions is equal to theelectron The charge number of lose shells that electrons that the atom has lost Lost 3 e electrons 3+ are either completely In equations the charge is usually shown above 2+or). else full and to the right of the symbol. (E. g. Mg empty © Boardworks Ltd 2003

The Electrons in a Sodium Ion In the sodium atom Atomic number = number of protons Number of electrons = 11 Na 23 = 11 Na+ Bye! Electron lost Electron arrangement: 2. 8. 1 (Incomplete Shell) Electron arrangement: 2. 8 (Full Shells) © Boardworks Ltd 2003

The Electrons in a Magnesium Ion In the magnesium atom Atomic number = number of protons Number of electrons = 12 24 = 12 Mg 12 Bye! Mg 2+ Mg Bye! Electron arrangement = 2. 8. 2 (Incomplete shell) 2 electrons lost Electron arrangement 2. 8 (Full Shells) © Boardworks Ltd 2003

Activity The Lithium Ion • How many electrons? 3 • How many electrons in the first shell? 2 • How many electrons in the second shell? 1 What electron arrangement? 7 Li 3 2. 1 1 st Shell = 2: full 2 nd Shell = 1: not full How many electrons to lose? New electron arrangement? Include a diagram 1 Li Li+ Bye! 2. (0) © Boardworks Ltd 2003

Activity The Boron Ion • How many electrons? 5 • How many electrons in the first shell? 2 • How many electrons in the second shell? 3 What electron arrangement? 11 B 5 2. 3 1 st Shell = 2: full 2 nd Shell = 3: not full How many electrons to lose? New electron arrangement? Bye! 3 BB 3+ Bye! 2. (0) © Boardworks Ltd 2003

Negative Ions. • These are ions formed by the atom gaining one or more electrons. Gain 1 e • They are called anions This is because during It is nearly Ions usually electrolysis they move towards the anode. always non- have metal OUTER The charge number of atoms that on the ions is equal to theelectron gain electrons that the atom has gained shells that Gain 3 e electrons 3 are either completely In equations the charge is usually shown above 2 - or and to the right of the symbol. (E. g. . Ofull ). else empty Gain 2 e • • - 2 - © Boardworks Ltd 2003

The Electrons in a Sulphide Ion. In the sulphur atom Atomic number = number of protons Number of electrons = 16 32 S = 16 16 S 2 - S 2 electrons gained Electron arrangement: 2. 8. 6 (incomplete shell) Electron arrangement 2. 8. 8 (Full shells) © Boardworks Ltd 2003

The Electrons in a Fluoride Ion. In the fluorine atom Atomic number = number of protons Number of electrons = 9 19 =9 F 2 - F 1 electron gained Electron arrangement: 2. 8. 7 (incomplete shell) Electron arrangement 2. 8. 8 (Full shells) © Boardworks Ltd 2003

Activity The Oxide Ion • How many electrons? 8 • How many electrons in the first shell? 2 • How many electrons in the second shell? 6 What electron arrangement? 16 O 8 2. 6 1 st Shell = 2: full 2 nd Shell = 6: not full How many electrons to gain? 2 New electron arrangement? 2. 8 OO 2 - © Boardworks Ltd 2003

Drag the words at the top to their correct places in the sentences. ©

1. Which of the following is not a subatomic particle? A. B. C. D. Proton. Isotope. Neutron. Electron. © Boardworks Ltd 2003

2. The element Cobalt has a relative atomic mass of 59 and an atomic number of 27. Which of these is a true statement about each neutral cobalt atom? A. B. C. D. It contains 59 neutrons. It contains 27 electrons. It contains 32 protons. It contains equal numbers of neutrons and electrons. © Boardworks Ltd 2003

3. The Periodic Table displays iron as shown below. This indicates that Fe atoms: 56 A. B. C. D. Fe contain 56 neutrons. 26 contain 30 electrons. contain 26 protons. contains more protons than neutrons. © Boardworks Ltd 2003

4. Bromine consists of a mixture of two isotopes: Bromine-79 and Bromine-81 • Which of the following is true: 80 Br A. B. C. D. 35 Both isotopes contain 35 protons. Bromine 79 contains 46 neutrons. Bromine 81 contains 44 neutrons. Bromine-81 is more reactive than bromine 79. © Boardworks Ltd 2003

5. Natural boron consists of approx. 20% boron-10 and 80% boron-11. • What will the relative atomic mass of natural boron will be? ? A. B. C. D. 10. 0 11. 0 10. 5 10. 8 B 5 © Boardworks Ltd 2003

6. Which answer best describes the shell arrangement of the electrons in a sodium atom? 23 Na 11 A. B. C. D. 2, 8, 1. 2, 2, 7. 2, 8, 8, 3. 2, 8, 8, 1. © Boardworks Ltd 2003

7. Which answer best describes the shell arrangement of the electrons in an oxygen atom? 16 O A. B. C. D. 2, 8, 6. 2, 8, 8. 2, 6. 8 © Boardworks Ltd 2003

8. Which of these elements will have electron shells that are either full or empty (i. e. not partially full)? A 14 N B 7 C 40 Ca 20 40 Ar 18 D 27 Al 13 © Boardworks Ltd 2003

9. Which answer best describes the shell arrangement of the electrons in an oxide ion O 2 -? 16 O A. B. C. D. 2, 8, 6. 2, 8, 8. 2, 6. 8 © Boardworks Ltd 2003