Trends in the Periodic Table — Transcript

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1. 0:03hi in this video we're looking at trends
2. 0:05in the periodic table and a trend is
3. 0:08just a pattern so if we look in the
4. 0:09periodic table from top to bottom within
5. 0:11a group we might see a pattern for a
6. 0:13certain property similarly if we look
7. 0:15left to right within a period in the
8. 0:18periodic table we might also see a trend
9. 0:20in a certain property and so we're gonna
10. 0:21look at three properties the first
11. 0:23property is something called atomic
12. 0:24radius
13. 0:25the second is ionization energy and the
14. 0:28third is electronegativity so let's
15. 0:31start with just what is atomic radius
16. 0:33atomic radius is the size of the atom
17. 0:35it's actually physically the radius of
18. 0:38the atom itself the distance from the
19. 0:39nucleus to the furthest out electron in
20. 0:42the electron cloud and so if I just look
21. 0:44at Group one here from hydrogen to
22. 0:46cesium and I look at how many electron
23. 0:49shells are occupied by electrons in
24. 0:52hydrogen I really only see that there's
25. 0:54one electron shell because there's only
26. 0:56one electron so we only need one shell
27. 0:59to house that one electron if I look at
28. 1:01lithium though lithium has three total
29. 1:04electrons that means two of those
30. 1:06electrons can fit in the first shell but
31. 1:08the third will have to go into the
32. 1:09second shell so lithium has two shells
33. 1:12and as you kind of go from top to bottom
34. 1:14in this group we see that we just have
35. 1:16an increasing number of electron shells
36. 1:19because the electron amount is going up
37. 1:21and we need more room to house those
38. 1:24electrons the way that we house those
39. 1:26electrons in an increasing amount is by
40. 1:28just bringing in more electron shells to
41. 1:30hold them and what you can see is that
42. 1:32as we go top to bottom there is a bigger
43. 1:35radius because we have more and more
44. 1:36electron shells the way to remember this
45. 1:39just quickly is to think of a snowman if
46. 1:41you look at these bottom three here you
47. 1:42see a snowman that was always my trick
48. 1:44for remembering this and I'm sure it's
49. 1:45plenty of other people's too it can be
50. 1:47yours but the reason that that's
51. 1:50happening is because there are more and
52. 1:51more electron shells as we go from one
53. 1:54period to the next down a group let me
54. 1:56lay out the atomic radius for all of the
55. 1:59elements on the periodic table what we
56. 2:00see is that top to bottom trend of the
57. 2:03atomic radius increasing but what you'll
58. 2:06also see is that as we go from left to
59. 2:09right within a period the atomic radius
60. 2:10actually decreases now
61. 2:13may seem strange to you because if we're
62. 2:15adding electrons as we go top to bottom
63. 2:17and that's causing our radius to get
64. 2:19bigger shouldn't our radius get bigger
65. 2:22as we go from left to right in a period
66. 2:23because in that situation we're also
67. 2:26adding electrons the explanation for
68. 2:27this one is a little more complicated so
69. 2:29let's just take a look at the elements
70. 2:31in period two lithium to neon lithium
71. 2:36has three protons and three electrons as
72. 2:38I slide over from lithium to neon I'm
73. 2:41adding one more proton but I'm also
74. 2:44adding one more electron and as that
75. 2:47happens the attraction of the electrons
76. 2:50to the nucleus becomes greater and
77. 2:53greater and that causes the entire
78. 2:54electron cloud to just kind of scoot you
79. 2:57in closer to the nucleus so you can see
80. 2:59of this grouping here neon is actually
81. 3:03the smallest atom and lithium lithium
82. 3:05lithium is the biggest atom in period
83. 3:09two so now we have our full trend here
84. 3:12top to bottom in a in a group the atomic
85. 3:15radius is going to increase think of the
86. 3:17snowman effect there the radius actually
87. 3:20decreases as we go from left to right
88. 3:22within a period so the overall trend if
89. 3:24you think of it this way this may help
90. 3:26you helium is the smallest atom and
91. 3:28francium or a caesium that would be on
92. 3:31this slide here but francium is the
93. 3:33largest atom and so knowing this trend
94. 3:35you can actually get a lot of the
95. 3:37information for the other two properties
96. 3:39we're looking at ionization energy as
97. 3:42the next property we'll investigate
98. 3:44ionization energy has a fancy name but
99. 3:47it actually is not all that fancy when
100. 3:50you know what it is ionization energy is
101. 3:52the amount of energy needed to remove an
102. 3:55electron from an atom you can think of
103. 3:57this almost like it's the cost of taking
104. 3:59an electron from an atom a low
105. 4:01ionization energy means it's really easy
106. 4:04to take an electron from that atom a
107. 4:06high ionization energy means it's more
108. 4:08difficult now here's the overall idea
109. 4:10the smaller and atom is the harder it is
110. 4:14to remove an electron from it if I just
111. 4:16look at an extreme case where I have a
112. 4:18small atom the valence electrons are
113. 4:21really close to the nucleus in this
114. 4:23scenario but if I have a larger atom the
115. 4:25valence electrons are much
116. 4:27farther away from the nucleus and
117. 4:28therefore they're much more willing to
118. 4:30kind of be donated to somebody else
119. 4:33another effect that's going on here is
120. 4:36the fact that we have all of these rings
121. 4:38that contain electrons already and so
122. 4:40this is called shielding shielding is
123. 4:42where the interior electrons kind of
124. 4:45mitigate the attractive force of the
125. 4:48nucleus the outside valence electrons so
126. 4:51said differently the signal is kind of
127. 4:54being blocked by the middle electrons
128. 4:56and so the valence electrons are not as
129. 4:58loyal to the atom and so it's much
130. 5:02easier to steal from a bigger atom as
131. 5:03compared to a smaller one now if we know
132. 5:07the trend in atomic radius in the
133. 5:09periodic table and we know that the
134. 5:11bigger the atom is the easier it is to
135. 5:13steal from it and therefore the lower
136. 5:14lianas ation and energy is required then
137. 5:17we can figure out what the trend in
138. 5:19ionization energy would be just based on
139. 5:22knowing the size of the atoms across the
140. 5:24periodic table the ionization energy is
141. 5:26going to increase from left to right
142. 5:28because if you just compare the size of
143. 5:30lithium for example to the size of neon
144. 5:33this is much more difficult so higher
145. 5:36energy over here because the size is
146. 5:40smaller those electrons are being held
147. 5:43really tightly to that nucleus lithium
148. 5:46not as much as neon so that means lower
149. 5:48energy over this way and remember the
150. 5:51lower the energy requirement the easier
151. 5:54it is to take an electron from that
152. 5:56particular element if we know that from
153. 5:58left to right across a period and it's
154. 6:00really just based off of the size then
155. 6:02we can also figure out what the pattern
156. 6:04is from top to bottom and a group for
157. 6:06ionization energy it's at the ionization
158. 6:08energy energy decreases so again the
159. 6:11bigger the atom the easier it is to
160. 6:13steal from it and that means the lower
161. 6:17the ionization energy will be okay so
162. 6:20the last piece is going to be
163. 6:21electronegativity electronegativity is
164. 6:23going to come back when we talk about
165. 6:25bonds and bond types so this is
166. 6:28something that is certainly important to
167. 6:30know it's going to help you when we when
168. 6:31we talk about bonds but in an
169. 6:33electronegativity
170. 6:34what we're talking about is how much an
171. 6:36atom wants an electron so it's a measure
172. 6:39of an atoms
173. 6:40action two electrons and it's based on a
174. 6:42scale from zero to four where four is
175. 6:45the element that really really wants
176. 6:47electrons and zero is an element that
177. 6:50really really does not want electrons so
178. 6:53let's look back at the periodic table we
179. 6:55fill in all the atomic radii for each of
180. 6:57the elements here I'd actually just like
181. 6:59to look at kind of the two extreme
182. 7:01scenarios here let's let's compare
183. 7:03lithium to fluorine fluorine has seven
184. 7:07valence electrons
185. 7:08if fluorine can just gain one more
186. 7:11valence electron it'd be a lot like neon
187. 7:13and that would fill its valence shell it
188. 7:16would satisfy the octet rule and
189. 7:18fluorine would absolutely love to gain
190. 7:20an electron there four fluorines
191. 7:22electronegativity is going to be really
192. 7:24high in fact fluorine has the highest
193. 7:26electronegativity of all the elements on
194. 7:28the periodic table now contrast that
195. 7:30against lithium they're in the same
196. 7:31period but lithium is on the other side
197. 7:34of the periodic table the left side
198. 7:35lithium has one valence electron and
199. 7:38does not want to gain any more valence
200. 7:41electrons in fact lithium would actually
201. 7:43prefer to lose that one valence electron
202. 7:45to become a lot like helium and so the
203. 7:49electronegativity for lithium and for
204. 7:51all the elements on sort of the left
205. 7:53side of the periodic table is going to
206. 7:55be far lowers let's take a look at it
207. 7:57just a special periodic table that only
208. 7:59shows the electronegativity values if
209. 8:01I'm yellow I really don't want electrons
210. 8:04in this periodic table and if I'm red
211. 8:05that means I really do again let's look
212. 8:08at fluorine three point nine eight
213. 8:10compared to lithium's point nine eight
214. 8:12there it is
215. 8:14and so if I just kind of look from left
216. 8:16to right within a period I'm gonna see
217. 8:19that the electronegativity increases if
218. 8:21I go top to bottom in a group the
219. 8:24electronegativity actually decreases and
220. 8:26this again unsurprisingly
221. 8:28has a lot to do with the radius of the
222. 8:31atom if I just kind of look kind of down
223. 8:33this way here all of these halogens
224. 8:36would like to gain one electron to be
225. 8:37like their noble gas neighbors it is
226. 8:41much easier for fluorine to attract an
227. 8:44electron that isn't originally its own
228. 8:46because fluorine is so small its nucleus
229. 8:49is located very close to its valence
230. 8:51shell as you go from top to bottom the
231. 8:53nucleus
232. 8:54gets further and further tucked in the
233. 8:56center the valence electrons get kind of
234. 8:59further and further out so the
235. 9:01electronegativity actually is a little
236. 9:03bit lower as we go top to bottom not
237. 9:05because they don't want that one
238. 9:07electron but because they're pull on
239. 9:09neighboring electrons is a little lower
240. 9:12because they're just bigger atoms and so
241. 9:15that's what's going on top to bottom in
242. 9:16a group on the periodic table for
243. 9:18electronegativity so that's it those are
244. 9:21the three trends in the periodic table
245. 9:22it's important that you know what the
246. 9:24trends are for sure but I believe it is
247. 9:27way more important that you know why
248. 9:29these trends exist and if you think
249. 9:31about it long enough it really all boils
250. 9:33down to the size of the atoms in many
251. 9:36cases it's about the distance between
252. 9:38the nucleus and the valence electrons
253. 9:41thank you
254. 9:46[Music]