Science Unit 4
Water Notes
- When boiling water, molecules are separated, not H and O - A.M.U. of water: 18, A.M.U of carbon dioxide: 44⇒ Boiling point of water VERY high compared to other molecules of the same size because it's so polar - Normally the greater the mass of the molecule the higher the boiling point, but water MAJOR exception because of polarity - Ice is less dense than liquid water (icebergs float in the ocean), everything else has higher density when solid than liquid - Vacuum in middle of solid water, forms in 6 sides with vacuum in middle - When heated up, molecules crumple into each other since still attracted which leaves a smaller, more dense space - Hydrogen bonds stronger when solid, weaker when liquid
Malleable material
-one that can be hammered or rolled into flat sheets and other shapes
Ductile material
-one that can be pulled out, or drawn, into a long wire
Properties of ions:
1.) Forming crystals: because they combine in repeating pattern 2.) High melting and boiling points: very strongly attracted since opposite charges 3.) Dissolve in water/conductive in water: water=polar → water breaks apart ionic compound to individually charged parts (ions)→ moves around freely charged so electrical current 4.) Brittle/shatter: opposite charges are aligned in crystal formation→ when moved same charges line up→ repel and shatter instead of bending Metal and nonmetal Transition metals can form ionic bonds Roman numerals: charge of transition metal (positive), only used with transition metals to verify because transition metals can have more than one charge (ex: iron (Fe) can either be +2 or +3)
Hydrogen bond
A chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom. (especially a nitrogen, oxygen, or fluorine atom)
Electronegativity:
Based on nuclear charge and number/location of electrons present in orbitals More protons → more pull an atom has four more electrons More electrons→ farther from nucleus → experience less positive charge (farther away and bc other electrons in lower orbitals will try to shield valence electrons away from nucleus) High inclination to grab electrons from other ions. -ability to draw electrons to itself
Why are ions brittle and shatter instead of bend?
Because the compound is held together by opposite charges attraction. When A force moves the atoms, two like charges could become next to each other due to the ions crystal shape. Like charges repel each other so the ion shatters because so many like chargers end up next to each other when a force moves the atoms. They are hard and brittle because of the strength of their ionic bonds and the attractions among all the ions.
How does water's polarity contribute to the properties of adhesion (sticks to other things), cohesion (sticks to itself), and water's ability to dissolve salt and other ionic compounds?
Cohesive → oxygen is more electronegative than hydrogen so gets slightly neg charge and h gets slightly positive → pos charge h then gets attracted to neg o of another water molecules Not that adhesive bc attracted to itself (NOI ITS ADHESIVE) Can dissolve salt bc pos charged Na is attracted to neg charged O and neg Cl is attracted to pos H
Polarity:
Difference of electronegativity in a bond Partial positive charge in one molecule and partial negative charge in another Ex: water molecule=electrons from hydrogen pull closer to oxygen molecules→ oxygen has slightly negative charge
Alloys
Homogeneous mixture (solution) made 2+ elements that has the properties of a metal Generally stronger than pure metals and are less likely to react w/ air or water Phys props--can differ from metals mixed, but depending on the way they are mixed alloys can retain many of the properties Ex. pure gold= shiny and easily bent so combines w/ hard metal (Cu or Ag) in coins and jewelry → much harder than pure gold but still retain beauty and shine Chem properties → combine elements to have better chem props (not reacting w air/ water) Ex. iron= good for making tools but always rusts so alloyed w 1+ elements to make steel → steel tools are as strong as iron but do not rust as much as iron Ex. stainless steel (iron, carbon, nickel, chromium) forks and spoons → iron normally reacts w water but when alloyed it does not so allows forks/spoons to be rinsed over and over again without rusting
Lewis Structure of Covalent Bonds
How to draw lewis structure: 1.) Count total number of valence e- in molecule 2.) Determine the central atoms. H must always go on outer edge because it can only form one bond 3.) Place the most electronegative atoms (halogens) on outside of structure 4.) Draw single bonds to connect atoms 5.) Assign e- to outermost atoms to complete their octets 6.) Assign leftover e- to central atoms 7.) Adjust bonds and e- to complete octets of all atoms (remember that B can have a sextet rather than octet)
Explain covalent bonding
In covalent bonding, atoms seek to fill their outermost electron orbital by sharing electrons.
What are the properties of ionic compounds? Covalent compounds? How does the bonding of these compounds explain these properties?
In ionic=take and opposite charges so attraction is very strong→ hard to break (high melting point) and only snaps or else like charges would be next to each other if bend In covalent=share electrons, low melting and boiling because not very strong bond, soft/bends because bond, not conductive
Why do ions have high melting and boiling points?
Ionic bonds have high melting and boiling points because their bonds are very strong so more energy is needed to break their bonds, causing them to become a liquid or gas. On the other hand, covalent bonds are weaker so less energy is needed to break them apart.
Compare and contrast nonpolar and polar covalent bonds.
Ionic compounds are so polar that they take and cannot share while covalent bonds are not that polar so they can share the electrons. Some covalent bonds, like H20, are still polar which means that electrons tend to spend more time around one molecule than the other, so that molecule becomes slightly negative/and slightly positive Polar=more electrons on one side of compound nonpolar=shared evenly
Bonds (Notes):
Ionic compounds form bonds by transferring valence electrons, or the electrons on an atom's outermost shell. Atoms in general want to get a place where they have to use the least amount of energy and are stable. In order to do this, they need to fill their outermost orbital to the maximum. Ionic compounds form between two elements that can bond because the number of valence electrons one needs to lose and the other needs to gain matches up perfectly. For example, in sodium chloride, or salt, sodium only has one valence electrons on its outermost shell so it wants to lose it while chloride needs one more to fill its outermost shell so it wants to gain one. When they lose or gain that amount of electrons, they have the same opposite charge and are attracted to each other. The amount of valence electrons on an atom's outermost shell determines the reactivity of that atom.
How is the formation of an ionic bond different from the formation of a covalent bond?
Ionic= give and take electrons Covalent=Share electrons
Describe the different characteristics of a metallic, ionic, and covalent bonded compound
Ionic=lose/gain electrons and opposite forces attract. Metallic=attraction when loose electrons and gain over and over Covalent=don't lose, share electrons
Why do ions form crystals?
Ions forms crystals because of the way they bond together, creating crystal formations. The ions form in a unique repeating pattern so that opposite charges are next to each other while like charges are not. Opposite charges need to be next to each other because they attract and will hold the compound together. The pattern formed by the ions remains the same no matter what the size of the crystal is.
Polyatomic Ion
Ions that are made of more than one atom that have an overall positive or negative charge In a polyatomic ion, the group of covalently bonded atoms carries a net charge because the total number of electrons in the molecule is not equal to the total number of protons in the molecule EX: Bicarbonate→ HCO3- Use parenthesis to represent amount of polyatomic ion ex: C(OS2)2 represents two of the atoms OS2 who are already bonded together (sorry those are supposed to be subscripts)
Explain metallic bonding
Metal atoms have a very loose hold on their electrons, so some electrons leave to go to another atom. That atom then becomes positive, and attracts other electrons. This becomes an ongoing cycle, until many atoms are "bonded" together.
Metallic Bonding
Metals found in crystals → metal atoms are very close to each other and in specific arrangements Bond between two metals Sharing of detached electrons ("sea" of electrons) Valence electrons=held loosely because metal wants to get rid of it→ leaves→ now the atom is positively charged (metal ion) and positive nucleus attracts the electron back to it Becomes many free electrons surrounded by positive metal atoms Electrons act as glue and hold many metal ions together
Explain why a water molecule is structured the way it is, with the hydrogen molecules diagonal form the oxygen molecule rather than them being in a straight line.
Negative forces (like forces) try to be separate from each other, straight line doesn't do this The oxygen has 6 valence electrons and thus needs 2 more electrons from 2 hydrogen atoms to complete its octet. This then leaves two lone electron pairs that are not bonded to any other atoms. The two hydrogen atoms and the two lone electron pairs are as far apart as possible at nearly 109o bond angle
Metallic Properties
Sea of electrons explains ability to change shape, conduct electric current, luster, and ability to conduct heat Malleable/ductile (flexible, stretched, pushed, compressed) → positive ions are attracted to all of the negative electrons around them so when hammered the ions are pushed but still lined up Electrical Conductivity→ electrons in a metallic bond are moving freely around atoms Luster→ when light strikes valence electrons, they absorb the light and give it back off Heat Conductivity→ freely moving valence electrons transfer energy to nearby atoms and other electrons
Why do ions dissolve in water and are conductive in water?
When an ionic compound is in a solid crystal state, the particles are stuck in place and cannot move around. In order for the compound to conduct electricity, the particles must be able to move freely so that an electric current can travel. When an ion dissolves in water because a water molecule is very polar and breaks apart ions, the bonds between the ions are broken so can move freely and have a charge. They can move around freely in an electrical current and move heat or electricity to another object. In a solid the ions are tight and all around so they cannot move freely→ no electrical current.
Molecular Compound:
a compound composed of molecules
Metallic Bond
an attraction between positive metal ions and the electrons surrounding it (more electrons stronger bond will be)
Neutral
atom w/o charge
Single bond
atoms share one pair of electrons
Triple Bond
atoms share three pairs of electrons
Double bond
atoms share two pairs of electrons
Covalent Bond
chemical bond when two atoms share electrons -between two nonmetals -The attraction between the nucleus and the shared electrons is the force that holds the atoms together -poor conductors because don't have any electrons on give away -low melting/boiling points bonds are weak
Nonpolar Bond
covalent bond in which electrons are shared equally
Polar Bond
covalent bond in which electrons are shared unequally
Molecule
neutral group of atoms joined by covalent bonds
Stable
not reactive (outermost orbital is filled)
Crystal
orderly 3d pattern of ions or atoms in a solid
Unit cell
the smallest group of atoms of a substance that has the overall symmetry of a crystal
