Danyal Education. The Particulate Nature of Matter: Atomic Structure. Candidates should be able to:

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Alexia Williamson
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1 (Contact: ) The Particulate Nature of Matter: Atomic Structure Candidates should be able to: a) state the relative charges and approximate relative masses of a proton, a neutron and an electron b) describe, with the aid of diagrams, the structure of an atom as containing protons and neutrons (nucleons) in the nucleus and electrons arranged in shells (energy levels) (no knowledge of s, p, d and f classification will be expected; a copy of the Periodic Table will be available in Papers 1 and 2) c) define proton (atomic) number and nucleon (mass) number d) interpret and use symbols such as 12 C e) define the term isotopes 6 f) deduce the numbers of protons, neutrons and electrons in atoms and ions given proton and nucleon numbers * not in combined Science syllabus # not in N level Science syllabus 1

2 (Contact: ) Characteristics of sub-atomic particles Proton Electron Neutron Relative Charge Relative Mass 1 1 / (negligible) Location in nucleus in electronic shells outside in nucleus nucleus Symbol p e n Definitions: atoms An atom is the smallest particle of an element that has the chemical properties of that element. proton number The number of protons in an atom nucleon number The total number of protons and neutrons in an atom isotopes Isotopes are atoms of the same element with the same number of protons but different number of neutrons ion An ion is a charged particle formed when an atom loses or gains electrons Why is an atom electrically neutral? An atom has an equal number of positively charged protons and negatively charged electrons. The opposite charges cancel each other out, making an atom electrically neutral. Describe with the aid of a diagram, the electronic structure of a magnesium atom, labeling clearly the electrons, protons and neutrons. A magnesium atom has 12 protons and 12 neutrons in its nucleus. Hence, its relative mass is 24. It has two electrons in the first electronic shell, eight electrons in the second shell, and two electrons in the third shell (valence shell). Hence, its electronic configuration can be represented as (2,8,2). Inside an atom: Interpreting symbol of elements nucleon number / mass number 23 atomic number / proton number 11 Na chemical symbol Element name: sodium No of protons: 11 No of neutrons: 12 No of electrons: 11 Describe how electrons are arranged in an atom. Electrons are arranged in electron shells around the nucleus. The lowest energy shell must be filled first before filling the next energy shell. For each energy level, there is a maximum number of electrons that is allowed to occupy. 1 st shell: max 2 electrons 2 nd shell: max 8 electrons 3 rd shell: max 8 electrons (if atom has less than or equal to 20 electrons) max 18 electrons (if atom has more than 20 electrons) The electronic structure is the arrangement of electrons in an atom. 2

3 (Contact: ) Electronic Structure of the first 20 elements of The Periodic Table 3

4 (Contact: ) Why does an atom have a tendency to gain/lose electrons? Which sub-atomic particle is responsible for the chemical properties of an atom? Most atoms of elements do not have a stable electronic structure because their outermost shell is not completely filled, so they do not have the maximum number of valence electrons. Hence, an atom has a tendency to gain/lose electrons, so that its valence shell is filled. In doing so, it achieves the noble gas structure (or stable electronic configuration). What type of ions do metals / non-metals form? Metals lose electrons to form positive ions. Non-metals gain electrons to form negative ions. Formation of a positive ion: Formation of a negative ion: Electrons are responsible for the chemical properties of an atom. The readiness of an atom to lose/gain its valence electrons to form ions determines how reactive it is. The more readily an atom loses/gains valence electrons, the more reactive it is. What is valency of an atom? Valency refers to the number of valence electrons of an atom involved in chemical bonding. For eg, if an atom gains, loses or shares 2 valence electrons to form chemical bonds, its valency is 2. 4

5 (Contact: ) Examples of ions and their sub-atomic particles Symbol Charge Atomic No. No. of protons No. of neutrons No. of electrons Na O Ne Ca Cl K What is the s, p, d and f classification? It is a way of arranging the electrons according to a specific order. The s orbital set contains a single orbital, a single orbital can hold a maximum of 2 electrons, so each s orbital set can hold 2 electrons. The p orbital set contains 3 orbitals, and thus can hold a total of 6 electrons. The d orbital set contains 5 orbitals, so it can hold 10 electrons. The f orbital set contains 7 orbitals, so it can hold 14 electrons. The order of the orbitals are: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s. Eg the electronic configuration of iodine can be written as: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 5 From this configuration, we can re-write as: 2, 8, 18, 18, 7 Catch no balls? Don t worry, it s not in the O level syllabus! 5

( + and - ) ( - and - ) ( + and + ) Atoms are mostly empty space. = the # of protons in the nucleus. = the # of protons in the nucleus

( + and - ) ( - and - ) ( + and + ) Atoms are mostly empty space. = the # of protons in the nucleus. = the # of protons in the nucleus Atoms are mostly empty space Atomic Structure Two regions of every atom: Nucleus - is made of protons and neutrons - is small and dense Electron cloud -is a region where you might find an electron -is