Lecture 2 Chemistry Part 1 (Atoms) PDF

Fundamentals of Chemistry: Part 1 Atoms and Elements 4BICH001W Biochemistry Dr Sarah K Coleman Learning Goals 1) Understanding of basic atomic structure 2) Understanding of organisation of electrons in simpler elements 3) Able to represent electron configuration 4) A...

Fundamentals of Chemistry: Part 1 Atoms and Elements 4BICH001W Biochemistry Dr Sarah K Coleman Learning Goals 1) Understanding of basic atomic structure 2) Understanding of organisation of electrons in simpler elements 3) Able to represent electron configuration 4) Able to relate electron organisation to Periodic Table position The Chemistry of Us Structure of the atom Smallest unit of an element Central nucleus surrounded by one or more electrons An actual image of hydrogen atom with orbiting electron. Done with a quantum microscope. Stodolna et al (2013) Phys. Rev. Lett. 110, The annoying cartoon meme version. 213001 Which element is this? The atomic nucleus Contains PROTONs and (usually) NEUTRONs Both given a mass of ONE (atomic mass units) Proton has POSITIVE charge Neutron is NEUTRAL Held together by the NUCLEAR force Are atoms charged particles? Components of the Atom Protons and neutrons and electrons PARTICLE MASS CHARGE (Coulombs) Proton 1 + 1.6 x 10-19 Neutron 1 0 Electron 5.5 x10-4 - 1.6 x 10-19 (~ 1/1800) So, atoms are neutrally charged because?  Elements and Isotopes Atoms which have different numbers of protons and thus electrons are different ELEMENTS e.g. Hydrogen vs Helium Atoms which have the same number of protons (and so electrons) BUT different numbers of neutrons are ISOTOPES of the same element e.g. hydrogen, deuterium and tritium Isotopes of Carbon Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). The Periodic Table 1 2 3 4 5 6 7 8 How the elements are 1 organised: 2 First formulated by 3 4 Dmitri Mendeleev 1869 5 Columns are GROUPS 6 Rows are PERIODS https://www.rsc.org/periodic-table  Elements and Periodic Table Atoms which have different numbers of protons and thus electrons are different ELEMENTS e.g. Hydrogen vs Helium Atomic Mass is the mass of the element = number of protons + neutrons Atomic number is the number of protons indicates properties of an element and where it is located in Periodic Table Atomic mass will always be greater than atomic number  Atomic Mass and Molecular Masses Molecules are composed of atoms Molecular Mass is the TOTAL summed mass of each individual atom Atomic masses of each element are found from via Periodic Table An example: Carbon dioxide has molecular formula CO2 One carbon atom is 1 x 12.01 = 12.01 Two oxygen atoms are 2 x 16.00 = 32 So, CO2 molecular mass is 12.01 + 32 = 44.01 or 44 (to 2 signif. figures) Why is the given atomic mass of carbon not a whole number?  Some practice examples: Calculate the molecular mass of water, H2O Calculate the molecular mass of table salt, NaCl You will have a chance to practice others and have full explanations in the seminar sessions https://www.rsc.org/periodic-table Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). Molecular mass, moles and Avogadro’s Number Avogadro’s Number is 6.02 x 1023 One mole of ANY SUBSTANCE contains 6.02 x 1023 particles of that substance e.g. One mole of carbon will have 6.02 x 1023 carbon atoms; one mole of glucose will have 6.02 x 1023 glucose molecules. Scientists use moles as a counting unit of measurement Amount in moles = amount (in grams) RMM(in g/mol) (Relative molecular mass is the same number as the molecular mass you have previously calculated) How many moles would one mole of moles contain? Moles and Molarity: the relationship Moles are a unit of amount of a substance Unit written as moles or mol (there is no capital letter) C6H1206 + 602 6CO2 + 6H2O 1 mol 6 mol 6 mol 6 mol Molar is a unit of concentration of a substance Concentrations are an amount per volume Molar is defined as moles per litre (mol/L); written as Molar or M (note the capital HCl Cl + H - + letter) 5 mol/L 5 mol/L 5 mol/L 5M 5M 5M Moles and Molarity: the relationship Moles are a unit of amount of a substance This difference is ESSENTIAL Unit written as moles or mol Use the 6 wrong C H 0 + 60 12 6 1 mol 6 mol 2 units and 6CO + 6H O 2 2 6 mol 6 mol any calculation or answer Molar is a unit ofisconcentration WRONG of aand meaningless substance No marks gained! Concentrations are an amount per volume Molar is defined as moles per litre (mol/L); written as Molar or M HCl Cl - + H+ 5 mol/L 5 mol/L 5 mol/L 5M 5M 5M Remember, Molar is the number of moles per litre A One Molar solution  Periodic Table Organisation Elements in the same Groups (columns) have similar chemical properties https://www.sigmaaldrich.com/content/dam/sigma-aldrich/articles/biology/marketing-assets/periodic-table-elements.png  Electrons: their orbitals and shells The chemical properties and reactivity of an element is related to that elements number and organisation of its electrons Elements and molecules react by losing or gaining or sharing electrons The aim is to increase the molecules stability Electrons DO NOT whizz around the nucleus like a solar system Electrons exist in discreet regions – the orbitals (there are different types) within the shells (distance out from the nucleus) Electron Organisation Pauli Exclusion Principle: Orbitals Any orbital can hold a MAXIMUM of 2 electrons s p d All p orbitals full = 6 electrons Electron Organisation Orbitals are grouped into Shells families called shells (energy level) which are numbered. Closest to nucleus is 1st shell and so outwards. A group of equivalent orbitals is a subshell e.g. 2nd shell has two subshells; one with the single s orbital and other with three p orbitals  Electron Organisation Maximum number electrons 1st shell has one s orbital 2nd shell has one s orbital and three p orbitals 3rd shell has one s orbital, three p orbitals and five d orbitals Shells closest to the nucleus will fill first (lower energy to higher energy)  Electron Configuration: arrangement of electrons in the shells Helium Neon 2 protons 10 protons 2 electrons 10 electrons 1s2 1s22s22p6 https://www.rsc.org/periodic-table Core and Valance Electrons Core electrons: filled shells closest to nucleus Valence electrons: outermost shell electrons; will participate in chemical reactions Fluorine Lewis Dot structures indicate 9 protons valence electrons of an element 9 electrons 1s22s22px22py22pz1 1s22s22p5 Core electrons Valence electrons Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous).  Lewis Dot Structures and Periodic Table NOTE: the GROUP NUMBER in the Periodic Table corresponds to the number of VALENCE electrons for element  Valence Electrons and the Periodic Table The OCTET RULE Atoms will be more stable if they have FILLED s and p orbitals for their VALENCE electrons. Elements will lose or gain electrons from other atoms to achieve the full OCTET (outermost 8 electrons). NOBLE GASES are very stable – they have filled outer p orbitals Conversely, alkali metals and halogen gases are very reactive Electronegativity and Polarity Ability of an atom to attract electrons toward itself in a chemical bond Electronegativity of an atom is related to its ionisation energy (losing an electron) and electron affinity (gaining an electron) Electronegativity can be used to estimate if a given bond will be; non-polar covalent, polar covalent or ionic Pauling Scale Across a Period electronegativity increases Greater number of protons = greater attraction for electrons Electronegativity Decreasing electronegativity down a Group Atoms have more electron shells, so have a bigger radius.  Summary Location of an element in the Periodic Table give information about its properties and reactiveness Atomic masses are necessary to calculate molecular masses Molecular masses are related to moles of a substance via Avogadro’s number Elements are neutrally charged (protons balanced by electrons) Chemical properties of an element are related to organisation of its electrons The valance electrons are especially import for this Types of bonds between element are related to the relative electronegativity of them And you know never to draw a ‘solar system’ picture (unless it has stars and planets!) Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). MCQ quiz for Lecture 2: Fundamentals of Chemistry part 1(Atoms) Answers will be given in your Seminar sessions – with further discussion. You must attempt before your seminar session. These quizzes are part of your learning for the Biochemistry module They will aid your on-going studies at the University of Westminster  Q1) All elements have an atomic number and an atomic mass value. The Atomic Number will indicate what? a) The number of protons and neutrons and electrons in an atom of that element. b) The atomic number is always smaller than the atomic mass. c) The number of neutrons. d) The number of protons or electrons in an element. e) The number of isotopes of the element. Q2) The reactive properties of an element are largely due to what? a) The total number of electrons it contains. b) The number of valence electrons it contains. c) The atomic mass of the element. d) The atomic number of the element. e) The number of neutrons it contains. Q3) The states of matter are solid, liquid, gas and plasma. How many liquid elements are in the Periodic Table and what are they? a) Over half of the elements are liquid. b) None of the elements are liquid. c) Only two are liquid; mercury and bromine. d) Only three are liquid; mercury, bromine and francium. e) This is an unanswerable as neither temperature nor pressure have been specified within the question. Q4) The maximum number of electrons a single orbital can hold is? a) Two electrons. b) Four electrons. c) Six electrons. d) Eight electrons. e) As given by the Atomic number of the element. Q5) The atomic mass of chlorine is 35.45 (often rounded to 35.5). Why? a) A single chlorine atom has 35.45 neutrons. b) A single chlorine atom has 35.45 protons. c) A single chlorine atom has 35 neutrons and the electrons make up the 0.45 mass. d) There are isotopes of chlorine with differing amounts of neutrons. e) There are isotopes of chlorine with differing amounts of protons.