Decoding The Periodic Table: Mendeleev's Discovery & Organizing Elements by Groups

1. The Periodic TableChapter 7

2. Arranging the Elements Chapter 7- Section 1

3. Organization • If you walk into a market trying to find milk, where do you look for it?? - the dairy section of course!! • Now imagine if the market or any other store was not organized by categories how long it would take you to locate things!! • Well… in the 1860’s scientists had the same problem – they have about 60 known elements but no way of organizing them

4. Discovering a Pattern • Dmitri Mendeleev first discovered a pattern to the elements in 1869 • He first organized the elements by similar properties physical & chemical properties like density, melting points, appearance & reactivity. • Mendeleev noticed: • fluorine & chlorine are both gases at room temp & they irritate the lungs • silver & copper are both shiny & tarnish in air • Li, Na, & K all react explosively with water

5. Periodic Properties of the Elements • Finally Mendeleev ranked the elements by increasing atomic mass – a pattern emerged! • He noticed there was a repeating pattern in a “periodic” way with increasing the atomic mass • Just like a calendar – the week repeats every 7 days • He used his table to predict that elements with certain properties would be discovered later.

6. Mendeleev’s Prediction: Germanium

7. Changing the Arrangement • Henry Moseley determined the number of protons—the atomic number—in an atom. He then rearranged the periodic table by placing the elements in order of increasing atomic number. • He used the wavelengths of x rays emitted from heavier elements to determine how many protons they had in their nuclei.

8. Increasing atomic number Similar chemical properties

9. Decoding the Table • Each horizontal row of elements (from left to right) is called a period. • Each vertical column of elements (from top to bottom) is called a group,or family. • Horizontally, elements are in order of increasing atomic number. Vertically, elements with similar chemical properties are grouped in columns. Groups (families) Periods

10. The Periodic LaW • The periodic lawstates that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements. • All of the elements follow the periodic law.

11. Grouping the Elements Chapter 7 Section 2

12. Groups/Families • The elements in a group have similar properties because the atoms of the elements have similar numbers of valence electrons(electrons in their outer energy level). • In order to have a complete set of electrons in their outer level, atoms will often take, give, or share electrons with other atoms. Elements whose atoms undergo such processes are called reactive.

13. Reactivity • As a group metals easily lost electrons to become positively charged ions (cations). • Both nonmetals and metalloids generally take or share electrons, making them negatively charged ions (anions).

14. Group 1: Alkali Metals • Alkali metalsare elements in Group 1 of the periodic table. • Most reactive metals - their atoms easily lose the one electron in the outer level of their atoms. • So reactive that in nature they are found only combined with other elements • Other characteristics: soft, shiny, silver color, low density

15. Group 2: Alkaline-Earth Metals • Alkaline-earth metalsare elements in Group 2. They are less reactive than alkali metals are, but more reactive than other metals. • Atoms of alkaline-earth metals have two electrons in their outer level.

16. Groups 3-12: Transition Metals • Elements of Groups 3-12 are called transition metals. • Transition metals are less reactive than alkali metals and alkaline-earth metals. • The lanthanides and actinides make up two rows of transition metals that are placed at the bottom of the table to save space. lanthanides actinides

17. Groups 3-12: Transition Metals, continued • Transition metals have 1 or 2 electrons in the outer level of their atoms. So, the properties of the transition metals vary. • But because these elements are metals, they share the properties of metals. • In general, they are also very similar to one another and can be confused.

18. Group 13: Boron Group • The elements in Group 13 have 3 electrons in the outer level of their atoms. • Elements in Group 13 are reactive. • Group 13 contains one metalloid and five metals. Aluminum is the most common element in Group 13.

19. Group 14: Carbon Group • The elements in Group 14 have 4 electrons in the outer level of their atoms. Their reactivity varies. • Group 14 contains metals, nonmetals, and metalloids. • Diamond, graphite, and soot are all natural forms of the nonmetal carbon.

20. Group 15: Nitrogen Group • The elements in Group 15 have 5 electrons in the outer level of their atoms. Their reactivity varies. • Group 15 contains metals, nonmetals, and metalloids.

21. Group 16: Oxygen Group • The elements in Group 16 have 6 electrons in the outer level of their atoms. These elements are reactive. • It is relatively easy to accept 2 electrons • Group 16 contains metals, nonmetals, and metalloids.

22. Group 17: Halogens • The elements in Group 17 are called halogens. They have 7 electrons in the outer level of their atoms. • Halogens are very reactive because their atoms need to gain only one electron to have a complete outer level. • Fluorine is the most reactive nonmetal. • All halogens are nonmetals. • Most halogens are toxic to humans.

23. Group 18: Noble Gases • The elements in Group 18 are called noble gases.Atoms of noble gases have a full set of electrons in their outer level. • Helium has 2 valence electrons, all others have 8 valence electrons • Noble gases are relatively unreactive. These elements were first called inert gases. • All noble gases are nonmetals.

24. Hydrogen • The properties of hydrogen do not match the properties of any single group, so hydrogen is set apart in the table. • Hydrogen has one electron in the outer level of its atoms. Hydrogen is reactive. • Hydrogen is the most abundant element in the universe.