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chem 1 electron
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- 1monoisotopic element + notesa monoisoptic element is an element which has only a single stable isotope e.g. F, Na, Al, P
however most elements naturally occur as a mixture of isotopes with different size nuclei. - 2isotope defintionatoms of the same element with the same atomic number but different mass numbers (same number of protons but different numbers of neutrons)
same outer electrons therefore chemical identity
kinetic isotopic effect: heavier isotopes react slightly more slowly
physical properties can differ - 3physical properties of isotopesisotopes have different numbers of neutrons, they have different masses, which means slightly different physical properties e.g. melting/boiling points, density etc.
- 4chemical properties of isotopesisotopes have the same chemical properties because they have the same number of electrons/electronic structure and chemical behaviour is defined by number of electrons/electronic structure.
- 5physical properties- observed by examining a sample of a pure substance
- arise from molecular structure and strength of intermolecular interactions - 6chemical properties- observed in the course of a chemical reaction
- arise from the distribution of electrons around the atoms nucleus, particularly the outer/valence electrons - 7Which of the carbon isotopes above has the highest melting point and why?- carbon 12 has the greatest mass and therefore requires the most energy to increase the movement of particles in order to overcome their attraction forces
- 8mass spec- defintion- most elements naturally occur as a mixture of isotopes with different size nuclei and therefore mass numbers cannot be used to define the mass of various atom s in quantitative chemistry.
- the mass spec can be used to determine all the isotopes present in a sample of an element and to therefore identify elements. - 9RAM (Ar) definition- the RAM quoted on the periodic table is a weighted average of all the isotopes of an element based on their natural abundance.
- the RAM defines the mass of an atom as an average mass incorporating all isotopes. Ar values are relative to the isotope carbon- 12 and mathematically defined as: - 10RAM equation- average mass of 1 atom of an element/ 1/12th mass of 1 atom of carbon-12
- 11mass number (A) defintion-sum of the protons and neutrons in the nucleus; also called nucleon number
(A)= no. of p + no. of neutrons - 12atomic number (Z) defintionnumber of protons in the nucleus of an atom
if the number of protons in the nucleus changes, the element also changes. this happens naturally with radioactivity. - 13subatomic particlessubatomic particle: charge: relative mass
proton: +1: 1unit
neutron: 0 : 1 unit
electron: -1 : 1/1820 units - 14atom- is the smallest building unit of matter
- Based on the work of Bohr, Rutherford, Chadwick and Thompson the atom consists of a positively charged nucleus accommodating protons and neutrons with negatively charged electrons orbiting the nucleus in energy levels (shells) - 15atom pt2the number of positively charged protons and non-charged (neutrally) neutrons gives mass to the atom, and the number of each in the nucleus of the atom determines the element.
- 16electron repulsionwhen electrons are paired there is electron-pair repulsion which causes the energy of the electrons to increase. increased energy makes the electron easier to remove and therefore the ionisation energy decreases.
- 174s and 3d- transition metalthe 4s orbital becomes the higher energy orbital and the 3d orbital becomes the lower energy orbitals but this only occurs after the 4s orbital is filled due to electron repulsion.
so the 4s orbital is filled first because the empty 4s orbital is lower in energy, however electrons are removed from 4s orbital first because the full 4s orbital is higher in energy. - 18hunds rule- when in orbitals of equal energy electrons will try to remain paired
electrons will fill empty orbitals before pairing up with other electrons. this is because electrons are negatively charged and repel each other, so they minimise repulsion by occupying their own orbitals. - 19orbital defintiona region in space where there is a given probability (usually 95%) of finding a particular electron.
cannot specify the definite or exact position of an electron in an ATOM. - 20ELECTRONSelectrons surround the nucleus in specific regions of space called orbitals.
the outermost electrons determine the properties of the atom e.g. reactivity and ability to form bonds. - 21elementelement is a pure substance that is made of only one kind of atom such as N, Cu or Al etc.
- 22chemical compounda chemical compound is a substance that is made of two or more types of atoms which are chemically joined such as H2O OR CO2 etc.
- 23physical mixturea physical mixture contains two or more substances that are only physically mixed and not chemically joined such as air, a mixture of mainly nitrogen and oxygen.
- 24mass spec usesmass spectrometry is used:
- to find the relative atomic mass (Ar) of elements
- to find the relative molecular mass (Mr) of molecular compounds
- to identify elements and chemical compounds - 25mixturemost elements naturally occur as a mixture of isotopes with different size nuclei and therefore mass numbers cannot be used to define the mass of various atoms in quantitative chemistry.
- 26mass spec steps1. the sample is converted into positive ions, which are accelerated to high speeds in an electric field (to a constant kinetic energy).
2. the positive ions with higher m/z values take longer to move through the drift area than those with smaller m/z values. the ions are distinguished by different flight times.
3. the ions reach the detector and generate a small current. the size of the current is proportional to the abundance of the species.
the separation is based on the fact that the speed of an ion depends on its m/z charge ratio. - 27madelungs rulethe energy of an atomic orbital increases with increasing n + l. for identical values of n + l, energy increases with increasing n.
- 28aufbauelectrons enter the lowest available energy level first.
and subsequent electrons occupy higher energy sub-levels. - 29hundswhen in orbitals of equal energy electrons will try to remain unpaired.
- 30quantum mechanicschemical behaviour is governed by electron structure.
the QMT takes into the account the amount of energy each electron possesses and describes the atom mathematically using the Schrodinger equation.
the solutions of schrodinger equation give the probability of finding an electron in a given volume of space, called an atomic orbital. - 31based on quantum mechanics:1. electrons are arranged energetically in energy levels (shells) and sub-levels (sub-shells).
2. electrons within an electron level have a specific amount of energy.
3. the energy levels are called main or principal energy levels and are given the numbers 1,2,3,4,5,6..7.
4. the main energy levels contain sub-levels and each main energy level contains a different number of sub-levels. - 32sub-levelselectrons are classified energetically into 7 main energy levels
sublevel/no of orbitals (2l+1)/max no of electrons
s/1/2
p/3/6
d/5/10
f/7/14 - 33simplified electron structure- based on Bohr and Rutherford electrons are arranged in electron shells of various sizes.
- the first electron shell can hold a maximum of 2 electrons
-the second electron shell can accommodate a maximum of 8 electrons
- the third electron shell can be stabillised with 8 electrons although it can hold a maximum of 18 electrons
- these electron arrangements can be depicted using B-R diagrams - 34electron structure and chem behaviour- chemically, elements are classified into metals, non-metals and metalloids
- metals lose electrons and become positive ions
- non-metals gain electrons and become negative ions
- the chemical behaviour of metalloids is in between metallic and non-metallic
- group 0 elements, the noble gases, belong to non-metals, although these elements are mostly unreactive
- - 35electron structure and chem behaviour 2- electron structure governs chemical behaviour
-elements undergo chemical reaction in order to stabilise their outermost electron configuration.
-noble gases are unreactive because their outermost electron configuration is stable
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- UK CAT chemistry Fichas sobre chem 1 electron, creado por cup cake el 01/10/2024.
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