Electrons In Atoms Mr. O Brien (SFHS) Chapter 5 Standard 1D

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1 Electrons In Atoms Mr. O Brien (SFHS) Chapter 5 Standard 1D

2 Electrons in Atoms (std.1d) What are Bohr Models? planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus similar to the planets orbiting the Sun How are energy levels related to the periodic table? The periodic table is divided into 7 energy levels (they are the rows) Electrons of atoms are organized into these energy levels. (figure 2) The Bohr Model can explain how glow sticks work. When electrons fall from higher energy orbitals to orbitals closer to the nucleus, energy is released in the form of light. (figure 1) The diagram to the left shows a simple Bohr model. The orbitals indicate where electrons orbit around the nucleus. The orbitals, energy levels, are indicated by the rows on the periodic table. Main Points of Bohr Model 1. Electrons contain energy. 2. Smaller orbits have less energy than larger ones.

3 Electrons In Atoms (std.1d) 1. Look at the row number the element is in. Draw that many energy levels. 2. Starting from atomic # 1, insert the electrons into their appropriate level. i. For those between columns 3-12, place those electrons in the previous level. You try. Draw elements the following elements: magnesium, chlorine, calcium, iron, scandium, arsenic. (figure 1) The figure above shows energy levels divided into rows. Note: the electrons of the elements in the middle section are placed into the previous level. Magnesium-24 Chlorine-35 Calcium-40 Scandium-45 Arsenic-75 Iron-56 (figure 2) Examples of Bohr Models of several isotopes.

4 Electrons In Atoms (std.1d) What are Valence Electrons? Electrons in the outermost orbital Why are they important? 1. Atoms gain or lose valence electrons for bonding 2. Atoms in the same group have similar chemical properties because they have same # of valence é Is there a short cut to find Valence Electrons? Group # (column) represents amount of valence electrons. What are Electron Dot Structures? Simplistic way to represent an atom and its valance electrons (figure 2) The valence electrons of Sodium is being transferred to Chlorine to create a bond.. Examples of Electron dot Structures (figure 1) These elements are all in the same group (column) in the periodic table. Just by looking at them you can see they have similar properties.

5 Electrons In Atoms (std.1d) Octet rule: Atoms tend to gain, lose, or share e in order to acquire a full set of eight valence é (noble gas). Exception (helium) Having all their valence é (8) make noble gases stable! Ion: an atom that gains or lose ve to have a positive or negative charge. When atoms lose ve and form positively charged ions (cations) When atoms gain ve, they form negative charged ions (anions). Practice: How many electrons will oxygen gain/lose to become a noble gas? Identify the number of valence electrons for bonding in Magnesium. Identify the number of electrons chlorine can accept for bonding. All Elements Want To Be Like Noble Gases!

6 Bohr Model (HONORS) In addition to principle quantum #, the electrons are also organized into 4 sublevels. s,p,d,f The sub-levels indicate the shape of the electrons orbit. (see examples) (figure 1) The figure above shows the division of the periodic table according to sub-levels. First Four Principal Energy Levels Principal quantum number (n) Sublevels present 1 s 2 s p 3 s p d 4 s p d f (figure 2) The figure above shows the shapes of the sublevels. This is were the electrons are actually located. The s sub-levels are simple orbits around the nucleus. The p sublevels are areas above/below or on the side of the nucleus where electrons are located. The d sub-levels are similar but they protrude out in other angles outside the nucleus. (figure 3) A more accurate representation of an atom. Note electrons are located in different areas around the nucleus according to their sublevels.

7 Bohr Model (HONORS) (cont.) Another way to organize electrons following the periodic table. Rules to follow: The Aufbau Principle: each é occupies the lowest energy orbital available. (figure 1) Notice in the energy level diagrams that sub-levels d have more energy than the previous s group. Because the d sub-levels have more energy we must first place electrons in the s sub-level before the d sub-level.

8 Writing Electron Configurations (HONORS) Electron configurations are a way to organize electrons by indicating the following: i. the level they are in ii. the shape (sub-level) of the orbital iii. the number of electrons in that sub-level You try. Write the following electron configurations: carbon, neon, potassium, zinc, bromine. C 1s 2 2s 2 2p 2 Ne 1s 2 2s 2 2p 6 K 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Br 1s 2 2s 2 2p 6 3s 2 2p 6 4s 2 3d 10 4p 5 Writing abbreviated electron configurations. Substitute the last element from column 18/8A in your configuration. Ex: carbon [He] 2s 2 2p 2 You try. Write the previous examples using the abbreviated method. Ne [Ne] K [Ar] 4s 1 Br [Ar] 4s 2 3d 10 4p 5 (figure 1) See the images above and below for a visual explanation of writing electron configurations.

9 Honors Info Quantum: minimum amount of energy that can be gained or lost by an atom. Matter can gain or lose energy only in small, specific amounts called quanta. Photon: particle of electromagnetic radiation with no mass that carries a quantum of energy. Photoelectric effect: photons are kicked off by the metal when light with enough energy strikes it. Atomic Emission Spectrum: a set of frequencies of the electromagnetic waves emitted by atoms of the element. Each element atomic emission spectrum is unique and can be used to identify element.