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Download Atomic Radius - CHEMISTRY 1 CP
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Periodic Table & Trends Atomic Radius (pm) 250 Periodicity – the tendency to recur at regular intervals. For example: the return of the full moon every 28 days. 200 150 100 50 0 0 5 10 Atomic Number 15 20 I II III Periodic Law When elements are arranged in order of increasing atomic #, elements with similar properties appear at regular intervals. Atomic Radius (pm) 250 200 150 100 50 0 0 5 10 Atomic Number 15 20 Founding Scientists Russian chemist Dmitri Mendeleev proposed 1st periodic table where elements were arranged according to ATOMIC MASS. (1869) English chemist Henry Moseley revised periodic table and arranged elements according to ATOMIC NUMBER. (1913) Chemical Reactivity Groups or Families Similar valence e- within a group result in similar chemical properties 1 2 3 4 5 6 7 Chemical Reactivity 1 2 3 4 5 6 7 Alkali Metals Alkaline Earth Metals Transition Metals Halogens Noble Gases Periodic Trends Atomic Radius size of atom First Ionization Energy © 1998 LOGAL Energy required to remove one e- from a neutral atom. © 1998 LOGAL Atomic Radius Increases to the LEFT and DOWN 1 2 3 4 5 6 7 Atomic Radius Atomic Radius (pm) 250 200 150 100 50 0 0 5 10 Atomic Number 15 20 Atomic Radius Down a Group: Atomic Radius increases. Reason: Increasing the number of energy levels (shells) From left to right across a Period: Atomic Radius decreases Reason: There is an increase in the number of protons in the nucleus causing there to be more of an effective nuclear charge, thus, a greater pull on the orbiting electrons in question. Effective Nuclear Charge The effective nuclear charge (often symbolized Zeff or as Z*) is the net positive charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge by the repelling effect of innerlayer electrons. The effective nuclear charge experienced by the outer shell electron is also called the core charge. It is possible to determine the strength of the nuclear charge by looking at the . oxidation number of the atom Calculating the effective nuclear charge In an atom with one electron, that electron experiences the full charge of the positive nucleus. In this case, the effective nuclear charge can be calculated from Coulomb's law. However, in an atom with many electrons the outer electrons are simultaneously attracted to the positive nucleus and repelled by the negatively charged electrons. The effective nuclear charge on such an electron is given by the following equation: Zeff = Z – S Z is the number of protons in the nucleus (atomic number), and S is the average number of electrons between the nucleus and the electron in question (the number of non-valence electrons). Electronegativity Electronegativity – a measure of the ability of an atom in a bond to attract electrons. Imagine bonded atoms as being locked in a tug-of-war competition over the shared valence electrons. The atom’s ability to “tug” is its electronegativity. American chemist Linus Pauling designed a scale based on fluorine (F) and assigned it a value of 4.0 (this is the most electronegative element). Electronegativity From left to right across a Period: Electronegativity increases Reason: The number of protons in the nucleus increases, which increases the attractive force between the nucleus and the valence electrons Down a Group: Electronegativity decreases Reason: Shielding – this is caused by an increase in the number of energy levels. Electronegativity Electronegativity Increases UP and to the RIGHT 1 2 3 4 5 6 7 Ionization Energy Ionization Energy - the energy required to remove an electron from an atom. From left to right across a Period: Ionization Energy increases. Reason: More protons in the nucleus creating a greater effective nuclear charge on orbiting electrons. Down a Group: Ionization Energy decreases. Reason: Shielding Ionization Energy First Ionization Energy Increases UP and to the RIGHT 1 2 3 4 5 6 7 Electron Affinity The Electron affinity of a molecule or atom is the energy change when an electron is added to the neutral atom to form an anion (negatively charges ion). This property can only be measured in an atom in its gaseous state. Melting/Boiling Point Melting/Boiling Point Highest in the middle of a period. 1 2 3 4 5 6 7 Ionic Radius Ionic Radius Cations (+) lose esmaller Anions (–) gain e- larger © 2002 Prentice-Hall, Inc. Examples Which atom has the larger radius? Be or Ba Ca or Br Examples Which atom has the higher 1st Ionization Energy? N or Bi Ba or Ne Examples Which atom has the higher melting/boiling point? Li or C Cr or Kr Examples Which particle has the larger radius? S or 2S Al or 3+ Al
