1 / 54

Formula

Formula. The formula for water ( H 2 O ) is a combination of symbols and subscripts. H and O are the symbols for the two types of elements ( H ydrogen and O xygen) found in water. The 2 is called a subscript , representing the number of atoms present.

osma
Télécharger la présentation

Formula

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Formula The formula for water (H2O) is a combination of symbols and subscripts. • H and O are the symbols for the two types of elements (Hydrogen and Oxygen) found in water. • The 2 is called a subscript, representing the number of atoms present. • Note, there is an invisible 1 by the oxygen

  2. Molecular and Empirical Formula • a molecular formula indicates the total number of atoms  in one molecule • an empirical formula is the simplest whole number ratio of atoms in the compound. •  consider hydrogen peroxide (H2O2 ) as an example. The molecular formula is H2O2. the empirical formula is HO. (lowest ratio is 1:1) • In some cases the molecular formula and empirical formula are the same. • For example, both the molecular formula and the empirical formula for water is H2O. (the lowest whole number ratio is 2:1)

  3. The formula for glucose (a simple sugar) is C6H12O6.  Is this formula a molecular formula or an empirical formula? Explain how you know. Answer This is molecular because the empirical formula would be CH2O.

  4. CHEMICAL BONDING Cocaine

  5. Review of Valence Electrons • involves the valence electrons or outermost shell (or highest shell) electrons

  6. Review of Valence Electrons Number of valence electrons of a main (A) group atom = Group number

  7. Forms of Chemical Bonds • Chemical bonding is the force of attraction between atoms. • We will deal with two types of bonding: 1) Covalent Bonding 2) Ionic Bonding.

  8. Covalent Bonding (molecular compounds) • Co-valent (sharing of valence electrons) • the force of attraction between two or more non-metals • recall the position of non-metals to the right of the steps on the periodic table. • the two non-metals both want to gain electrons (to be like the noble gases), since both cannot gain electrons at the same time they share. • the unit formed by a covalent bond is called a molecule (it is neutral it has no charge) • H2O ,  CO2  , O2

  9. the unit formed by an ionic compound is a formula unit formula units are very complex crystal lattice arrangements the smallest crystal of sodium chloride is really (Na+)6(Cl-)6 to keep things simple we reduce this down to an empirical formula (lowest whole number ratio) of NaCl.

  10. Cl Cl Cl2 This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

  11. Student Work • A quick review of the period table.  Read 5.5 "Elements and the Periodic Table" on pages 184 - 187. Answer questions 2,3, 4 from "Understanding Concepts" on page 187 • Read 5.6 " How elements form compounds" on pages 188 - 187.  Answer questions: 1, 2a

  12. Naming and writing formulas for molecular compounds • We will deal with five categories of molecular compounds: 1.  Mono-atomic elements: mono - means one, so These are the non-metals that that exist in nature as individual atoms.

  13. 2.  Diatomic molecular elements As the heading suggest these are elements composed of two (di) nonmetal  atoms.  We seen these in the last lesson. (just remember the gen's)

  14. 3. Polyatomic molecular elements These are non-metal elements composed of many (poly) atoms.

  15. 4. Trivial Names: Common names. Despite the IUPAC rules for naming many molecular compounds still go by their trivial (common) names

  16. 5.  Binary Molecular Compounds These are molecular compounds that contain two different non-metal atoms. binary - 2 molecular - non-metal atoms only compound - two different atoms Carbon dioxide - CO2 is a common example. It consists of carbon atoms and oxygen atoms. The IUPAC rules for naming and formula writing involve use of a prefix system that indicates the number of atoms present.

  17. You must know this list (first ten prefixes) in order to convert formula to names or to convert names to formulas. What do you do when you are given the formula and you are asked to write the IUPAC name?

  18. Write a IUPAC name for CCl4. Answer The first element is C. Its full name is carbon. The second element is chlorine (Cl). Its name is shortened to chlor, and the prefix -ide is added to give chloride. The prefix mono (1) is added to carbon, and the prefix tetra (4) is added to chloride to give the name: monocarbontetrachloride. The prefix mono is omitted from the first element name to give carbon tetrachloride.

  19. Your turn: 1. What is the IUPAC name for CF4 ? The IUPAC name is carbon tetrafluoride. 2. What is the IUPAC name for SiO2? The IUPAC name is silicon dioxide. 3. What is the IUPAC name for SO3  ? The IUPAC name is sulfur trioxide. 4. What is the IUPAC name for P4S3 ? The IUPAC name is tetraphosphorus trisulfide.

  20. Your turn: Write the molecular formula for each of the following compounds: 1.  nitrogen triiodide NI3. 2.  triphosphorus pentabromide  P3Br5 3.  carbon disulfide CS2 4. sulfur trioxide SO3

  21. Student Work • Read 5.11 "Molecular Compounds" on pages 203 - 204. Answer questions 1 - 6 on page 204

  22. Ionic Bonding • the force of attraction between a metallic ion and a non-metallic ion. (or complex ion) • or, the force of attraction between a positive ion (cation) and a negative ion (anion). • ionic compounds are made up of two oppositely charged ions. • Examples:  • NaCl  (sodium chloride) • NaHCO3 (sodium bicarbonate - baking powder) • CaCO3 (calcium carbonate - rolaids/tums

  23. NaCl This is the formation of an ionic bond. - + Na Cl electron transfer and the formation of ions

  24. Energy Level Diagrams for Ions • Octet Rule • Atoms react by changing the number of electrons to try and get the same structure of the nearest noble gas. • In other words, atoms either gain or lose electrons to become stable.

  25. What's so special about the noble gases? The noble gases have their valence shells full of electrons: 2, 8, 8,... which represents stable arrangements of electrons. Examples: Fluorine (9)  would gain (1) electron to be like Neon (10) Magnesium (12) would lose (2) electrons to be like Neon (10)

  26. Simple Ions • Simple ions are atoms that no longer have equal numbers of electrons and protons. • As a result of this imbalance they now have a positive or negative charge

  27. Cation • A cation is  a positve (+) ion (clue: the t in cation resembles a + sign). •  Metal atoms lose electrons to become positive thus, metals form cations.  • Example:  Na+, Mg2+

  28. Anion • An anion is ANegative ION (A N ion) • Non-metal atoms gain electrons to become more negative thus, non-metals form anions:  • Example:   F- , O2-

  29. Let's consider magnesium:

  30. Let's look at phosphorus:

  31. Special Nature of hydrogen Hydrogen is special, it has a split personality! H can behave as a metal and lose electrons H+ H can also behave as a non-metal and gain electrons H-

  32. Your turn: 1.  What is the charge on the ion formed by Chlorine? 2.  What is the charge on the Aluminum?

  33. Student Work • Further reading on this see 5.6 pages 188 -192 • Energy level diagram worksheets. • Simple ion worksheet.

  34. Ionic Compounds Formula Writing/ Naming Ionic compounds are formed as a result of the attraction between oppositely charged ions.  Ionic bonding results from the transfer of electrons from one atom to another.

  35. There are three categories of ionic compounds that we will deal with. • 1) Binary ionic • simple ions (only single charges) • multivalent ions (more than one charge) • 2) Polyatomic ions (complex ions) • 3) Hydrates

  36. Binary Ionic compounds - simple ions: • Binary ionic compounds are composed of a metal ion (+)  and non-metal ion (-).  The word binary simply means only two ions are involved. Example: NaCl - the combination of a sodium ion and a chloride ion.

  37. Note: Do Not use prefixes - they are for molecular compounds (two non-metals. Ionic compounds are writing as empirical formulas (lowest ratio) Name the following: 1. LiBr Lithium Bromide 2. AlCl3 Aluminum Chloride 3.Rb2S Rubidium sulfide

  38. Writing Chemical Formulas for Binary Ionic Compounds: • Writing chemical formulas for binary ionic compounds relies heavily on your knowledge and understanding of ion charges in the periodic table.

  39. Example 1: What is the chemical formula for a compound that contains Potassiumions and Bromide ions. • Write down the symbols of the ions involved Potassium (group 1 thus has a 1+ charge) K+ Bromide (group 17 thus has a 1- charge)  Br - • 2. Determine the lowest whole number ratio of ions that will give a net charge of zero. • K+) x 1 = 1+          (Br -) x 1 = 1- •                 (1+)  +  (1-) = 0 net charge

  40. Write the formula removing all charges. • KBr • We normally do not write in the ones (1) Cross Multiply method:

  41. Example 2: What is the chemical formula for the ionic compound that contains magnesium ions and bromide ions. • 1. Write down the symbols of the ions involved Magnesium (group 2 thus has a 2+ charge) Mg 2+ Bromide (group 17 thus has a 1- charge)  Br - 2.Determine the lowest whole number ratio of ions that will give a net charge of zero. Mg2+) x 1 = 2+          (Br -) x 2 = 2-             (2+)  +  (2 -) = 0 net charge 

  42. 3. Write the formula removing all charges MgBr2 Cross Multiply method:

  43. Your Turn: Write the chemical formula for each compound: 1.  Sodium sulfide Na2S 2.  Aluminum Bromide AlBr3 3. Barium Iodide BaI2 Mg3N2 4.  Magnesium Nitride

  44. Multivalent Species • Ions of a certain elements can have more than one possible charge. Such elements are called multivalent species For example, copper is multivalent - its ions can have either a 1+ or a 2+ ion charge (Cu + or Cu 2+

  45. If you have not already noticed, these ions and there charges are provided on the period table! 

  46. Alfred Stock resolved this problem in an interesting way. He decided to use a Roman numeral in the cation name to indicate its charge. CuCl2 is named copper (II) chloride. (copper is in the Cu 2+ CuCl is named copper (I)chloride.  (the copper is in the  Cu+ It is often the case that one ion charge is more stable and therefore more common than another. For example, Cu2+ is more common/stable than Cu+.  This is easy to tell from the periodic table because they have the most common form of the ion written on top.Cu2+ is written above Cu+.

  47. Chemical Formulas Involving Multivalent Species: You have to indicate the charge of the multivalent species with roman numerals. Only use roman numerals for metals that have more than one charge!

More Related