Chemistry IS 4 (Chemical Reactions) (3. How do chemical reactions absorb…
Chemistry IS 4 (Chemical Reactions)
Bonding in a Chemical Reaction Activity
1. What holds atoms together in molecules?
Chemical Bonds as Attractions Between Particles
learn how elements combine to form new compounds, the forces that hold them together, the forces between particles and molecules, and the energy needed to break or form bonds
how do you teach this??!
Less of "ionic bonds result from the transfer of electrons from one atom to another and covalent bonds from the sharing of electrons between two atoms. students are then presented with differences in the two types of bonding. they conduct experiments to verify these differences
More of "observe
how materials behave on their own and with other substances
. They recognize patterns that allow them to determine that there
must be two different categories of materials
. They use evidence about the properties to infer the strength and properties of the bonds that hold the materials together" eventually label categories as ionic and covalent bonds
do you teach metal&nonmetal vs nonmetal&nonmetal? or a spectrum?
observations at the macroscopic scale give clues about the nature of chemical bonding.
conduct an investigation to measure the conductivity of different solutions (salts, acids, bases, hydrocarbons, and oxides) to gather evidence that there must be some relationship between electricity and material properties
use this evidence to support a model of different types of chemical bonds and attractions.
ionic model- includes attractions between charged particles related to
learn how the nucleus of one atom has enough attractive force to pull one, two, or three electrons away from nuclei that doesn't have the same attractive force on its own electrons
applying the principles of electrostatic attraction, students should be able to predict that the resulting cations and anions will be attracted to each other and form ionic bonds
if either ion feels a stronger attraction to a different particle, then the existing bond is easily broken. know that when salt dissolves in water, its bonds are broken, what can students infer about the charge of water molecules?
Pure materials with high boiling points are more likely to be bonded together more stably than materials with lower boiling points
where/when do you start talking about Coulomb's law?
3. How do chemical reactions absorb and release energy?
middle school- should've learned that chemical reactions can release and absorb energy
need to develop models that illustrate the release or absorption of energy from chemical reactions
begin model by relating back to investigations at the bulk scale, can build on their model of the ionic bond breaking between sodium and chlorine when salt dissolves in water
1st model of chemical reactions, original chemical bonds are broken and new bonds form
because these changes affect the distribution of energy within the chemical system, they must extend their model to include energy flows.
conduct investigations/analyze data to discover that some reactions appear to release energy while others absorb it
in a more detailed model of energy flow, all chemical reactions both absorb and release energy, just in differing amounts
can observe water temperature decrease when salt is added, even when both materials start at the same temperature
Does breaking the bond absorb energy from the water? When sodium mixes with water, students observe that it gives off a dramatic amount of energy as light and sound. Does sodium release energy when it forms new bonds?
Pouring Molten Salt into Water
Observations: the salt only exploded when it was super hot. borax, sodium carbonate, and boric acid into fish tanks- includes ionic compound- didn't explode- protected by leidenfrost effect. sodium alone exploded, but not as vigorously (still a msyery wy leidenfrost effect not seen in sodium chloride)
Chemical reactions involve separating two atoms (requiring work to overcome their attraction, like lifting a heavy load against gravity) and bringing a different combination of he atoms closer together (which releases energy, like how a falling ball converts gravitational potential energy to kinetic energy as it is attracted to the Earth and moves closer to it)
whether or not a chemical reaction gives off energy overall depends on the relative magnitudes of these two energies
the potential energy related to the relative position of two interacting atoms in a chemical bond is known as the "bond energy"
by comparing the bond energy of the products and the bond energy of the reactants, students can construct models of the energy in the system, and predict whether or not energy will be absorbed or released
ex. when salt dissolves in water, new attractions between water and the Na and Cl are weak, so the particles remain relatively far apart (releasing relatively little potential energy)
the temperature of water goes down when salt dissolves in it because much energy goes into breaking bonds, but less energy is released when the new attractions form
ex. formation of biomass from CO2 and water requires energy input.
2. Bonding (Ionic vs. Covalent)
as two nonmentals come close to one another, the orbitals overlap, trapping 2 electrons in the energy field, creating a
students need to explain the link between bulk effects and microscopic causes by developing models of how these bonds form
investigate other forms of attraction (polar attractions and intermolecular forces)
don't need to know by name, but should be able to investigate properties like surface tension and viscosity, and provide a model-based explanation o how these properties relate to microscopic electromagnetic attractions
need to develop and explain models of covalent, polar covalent, and ionic bonding
phenomena: hot and cold packs look identical on the outside, but use different ingredients to 'spontaneously' change their temperature warmer and cooler
two day lesson about modeling the energy in chemical bonds
distribute hot and cold packs, instructs students to flex the bags to feel the change in temperature using infrared thermometers, and record these changes in a collaborative online database