Can you recall… What is Matter? Matter is anything that has mass and takes up space.

Can you recall… What is the kinetic particle theory?

Can you recall… What is the kinetic particle theory? The Kinetic Particle Theory states that matter is made of tiny discrete particles (atoms or molecules), which are in constant and random motion.

So, what is an atom? solid liquid gas Atom!

So, what is an atom? An atom is the smallest unit of an element, having the properties of that element. Do you think a copper atom is identical to a zinc atom?

Are atoms like solid balls? With nothing else inside?

Subatomic Particles Atoms - made up of subatomic particles electron proton neutron nucleus positively charged neutral negatively charged Note: The nucleus consists of protons and neutrons

Subatomic Particles ParticleSymbolRelative Mass Charge Protonp11+ Neutronn10 Electrone-e- 1/ electron proton neutron nucleus positively charged neutral negatively charged

Thinking Time… Why is the term "relative mass" used rather than just mass? ParticleSymbolRelative Mass Charge Protonp11+ Neutronn10 Electrone-e- 1/18361-

Thinking Time… Hints… Mass of proton= ~1.67×10 −27 kg Mass of neutron = ~1.67×10 −27 kg Mass of electron= ~ 9.11×10 −31 kg

Thinking Time… Mass of proton, neutron and electron are too small and inconvenient to work with. By using relative mass, we do not have to remember the exact value of the various masses.

Counting protons… Proton Number The number of protons in an atom is called the proton number. Proton number is also known as the Atomic Number.

Counting protons & neutrons… Nucleon Number Nucleon number is the number of protons and neutrons in the nucleus of an atom. Nucleon number is also called the Mass Number.

Nucleon Number Nucleon (Mass) number = number of protons + number of neutrons

Carbon atom in symbol form: C. Can also be written as carbon

Question How many protons, electrons, and neutrons are there in a C atom? 6 protons, 6 electrons and 6 neutrons. 12 6

Worksheet Time… Try Question 1 to 4

The Atomic Model The centre of an atom is called the nucleus which contains the protons and neutrons. protons neutrons nucleus

The Atomic Model The electrons in an atom are arranged in shells (orbits) at different distances from the nucleus. Note: Shells are also called energy levels. protons neutrons nucleus 1 st shell2 nd shell3 rd shell 4 th shell electron

The Atomic Model 1 st shell 2 nd shell 3 rd shell 4 th shell electron Each shell can hold a certain maximum number of electrons. Advanced: For elements after calcium in the 4th period, their third shell can hold up to 18 electrons. (a) 1st shell - 2 electrons (b) 2nd shell - 8 electrons (c) 3rd shell - 8 electrons (1st 20 elements only)

Question An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus.

Question An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus. (a) Why is the atom electrically neutral? Number of electrons = number of protons. Equal positive and negative charges (b)Why is the nucleus positively charged? The nucleus contains protons and neutrons. Protons are positively charged while neutrons are electrically neutral.

Differentiating different elements How do I differentiate the atoms of one element from the atoms of another element? All atoms of the same element have the same number of protons while those of different elements contain different number of protons C Na vs

Worksheet Time… Try Question 5

Advanced: Isotopes Isotopes are atoms of the same element with different numbers of neutrons. -> same proton number, different nucleon number E.g. carbon has 3 isotopes: 12 6 C 13 6 C 14 6 C

Electron Arrangement Nitrogen-14 atom has 7 electrons 7 p 7 n Key - electron p - proton n - neutron Drawing the full electronic configuration Note: full electronic configuration of an atom shows the arrangement of electrons in different shells.

Electron Arrangement Nitrogen-14 atom has 7 electrons 7 p 7 n Key - electron p - proton n - neutron Writing the electronic configuration: 2.5 shows arrangement of electrons in different shells. 1 st shell 2 nd shell separate the 2 shells

Electron Arrangement Argon-40 atom has 18 electrons 18 p 22 n Key - electron p - proton n - neutron electronic configuration of 2.8.8

Valence Shell Valence shell - farthest occupied shell from the nucleus Valence electron - electron in the valence shell 7 p 7 n

Valence Shell Note: only valence electrons are involved in chemical reactions. 7 p 7 n

Outer electronic structure only valence electrons are drawn 7 p 7 n Key - electron p - proton n - neutron

Thinking Time… Based on what you have learnt in this topic, describe how are the elements in the Periodic Table being arranged? Arrangement of elements in the order of increasing proton (atomic) number.

Formation of Ions During chemical reactions, some atoms might lose/gain electron(s). Atom becomes an ion (charged particle) when it gains or loses electron(s).

Question Why does an atom become a charged particle when it gains or loses electron(s)? An atom is electrically neutral because number of electrons = number of protons (equal positive and negative charges). When it gains or loses electron(s), the positive and negative charges are not balanced. Therefore, the atom becomes a charged particle.

Formation of cations When an atom loses one or more electrons, it becomes a positively charged particle called cation. Lithium atom (Li) 3 electrons 3 protons Net charge: 0 Lithium ion (Li + ) 2 electrons 3 protons Net charge: +1

Formation of anions When an atom gains one or more electrons, it becomes a negatively charged particle called anion. Fluorine atom (F) 9 electrons 9 protons Net charge: 0 Fluoride ion (F - ) 10 electrons 9 protons Net charge: -1

Question for Thought Why do atoms become ions? To obtain a full valence shell To obtain the same electronic structure of a noble gas so as to be stable. (Note: this will be covered under chemical bonding)

Worksheet Time… Try Question 6 to 8

Exercise Charge of ionElementName of ionSymbol of ionNo. of electron gainedNo. of electron lost -2Oxygen Sulfur Oxide Sulfide O 2- S 2- 2 Fluorine Chlorine Fluoride Chloride F - Cl Hydrogen Lithium Sodium Potassium Hydrogen Lithium Sodium Potassium H + Li + Na + K Beryllium Magnesium Calcium Copper Iron Beryllium Magnesium Calcium Copper (II) Iron (II) Be 2+ Mg 2+ Ca 2+ Cu 2+ Fe Aluminium Iron Aluminium Iron (III) Al 3+ Fe 3+ 3

Exercise Do metals generally form cations or anions? cations Do non-metals generally form cations or anions? anions