Friday, Jan. 10 th : “A” Day Monday, Jan. 13 th : “B” Day Agenda Collect movie worksheet Begin Chapter 5: “Ions and Ionic Compounds” Sec. 5.1: “Simple Ions” Octet rule, ion, cation, anion In-Class: Section 5.1 review, pg. 165: #1-13 Homework: “Ions and Subatomic Particles” worksheet Concept Review: “Simple Ions” Next time: Quiz over section 5.1
Chemical Reactivity How much an element reacts depends on its electron configuration. Noble gases are the least reactive elements because their outer energy levels are full with 8 electrons. (except He, which is full with 2) In most chemical reactions, atoms try to match the electron configurations of the noble gases by either gaining or losing electrons. Most atoms want to become “noble”.
Chemical Reactivity Octet Rule: a concept of chemical bonding theory that is based on the assumption that atoms tend to have either empty valence shells or full valence shells of eight electrons. “ 8 is Great!”
*Alkali Metals and Halogens are the Most Reactive Elements* As members of Group 1, alkali metals have only 1 electron in their outermost energy level. By losing that 1 electron, an alkali metal can get an electron configuration like a noble gas, with 8 electrons in its outermost energy level. - 1 electron 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6 Which alkali metal is this? Potassium (K)
*Alkali Metals and Halogens are the Most Reactive Elements* Remember, potassium’s electron configuration was: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Question: Why doesn’t potassium gain 7 electrons to achieve a stable octet instead of losing 1? Answer: Removing 1 electron requires far less energy than adding 7 electrons.
Alkali Metals and Halogens are the Most Reactive Elements As members of Group 17, the halogens have 7 electrons in their outermost energy level. By gaining 1 electron, a halogen can get an electron configuration like a noble gas, with 8 electrons in its outermost energy level. + 1 electron 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 2 3p 6 Which halogen is this? Chlorine (Cl)
Valence Electrons After it loses one electron, potassium has the same electron configuration as chlorine does after it gains one electron. Both are the same as the noble gas argon. 1s22s22p63s23p61s22s22p63s23p6 The atoms of many elements become stable by achieving the electron configuration of a noble gas. Remember, the electrons in the outermost energy level are called valence electrons.
The Periodic Table Reveals an Atom’s Number of Valence Electrons To find out how many valence electrons an atom has, check the periodic table. Magnesium, Mg, has the shorthand electron configuration: [Ne]3s 2 The outermost energy level is the 3 rd energy level. This means that a magnesium atom has two valence electrons, located in the 3s orbital.
The Periodic Table Reveals an Atom’s Number of Valence Electrons The shorthand electron configuration of phosphorus, P, is: [Ne]3s 2 3p 3 The outermost energy level is the 3 rd energy level. This means that each phosphorus atom has five valence electrons: two in the 3s orbital and three in the 3p orbital.
Atoms Gain or Lose Electrons to Form Stable Ions All atoms are uncharged because they have equal numbers of protons and electrons. For example, a potassium atom has 19 protons and 19 electrons. After losing one electron, potassium still has 19 protons but now only has 18 electrons. Because the numbers are not the same, there is a net electrical charge.
Atoms Gain Or Lose Electrons to Form Stable Ions Ion: an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge. The following equation shows how a potassium atom forms an ion with a 1 + charge. K K + + e Cation: an ion that has a positive charge.
Atoms Gain Or Lose Electrons to Form Stable Ions In the case of chlorine, far less energy is required for an atom to gain one electron rather than lose its seven valence electrons to become stable. The following equation shows how a chlorine atom forms an ion with a 1 − charge. Cl + e → Cl Anion: an ion that has a negative charge
Characteristics of Stable Ions Both an atom and its ion have the same number of protons and neutrons, so the nuclei are the same. But, an atom and its ion have different numbers of electrons. The chemical properties of an atom depend on the number and configuration of its electrons. So, an atom and its ion have different chemical properties.
Many Stable Ions Have Noble-Gas Configurations (pg. 162)
Some Stable Ions Do Not Have Noble Gas Configurations Transition metals often form ions without complete octets. The stable transition metal ions are all cations. Some elements, mostly transition metals, can form several stable ions that have different charges…
Some Stable Ions Do Not Have Noble Gas Configurations (pg. 163)
**Metals Form Cations** Nearly all metals form cations, which means they lose electrons. For example, magnesium metal, Mg, has the electron configuration: 1s22s22p63s21s22s22p63s2 To achieve a noble-gas configuration, magnesium must lose two electrons. Losing two electrons requires less energy than gaining six. Atoms are lazy, just like us!
**Non-metals Form Anions** The atoms of all non-metal elements form anions, which means they gain electrons. For example, oxygen, O, has the electron configuration 1s22s22p41s22s22p4 To achieve a noble-gas configuration, oxygen must gain two electrons. Acquiring two electrons requires less energy than losing six.
In-Class/Homework In-Class: Section 5.1 review, pg. 165: #1-13 Homework: “Ions and Subatomic Particles” WS Concept Review: “Simple Ions” Next time: Quiz over Section 5.1
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