Your Question: There are two kinds of elements that didn't appear on the periodic table until after 1892. What kinds are they and why do you think it took so long to discover them?
The Answer: Moseley’s analysis enabled chemists to refine the table further and reveal more gaps, which suggested that there were more new elements waiting to be discovered, with atomic numbers 43, 61, 72 and 75. Scientists subsequently found these elements—now known as technetium, promethium, hafnium and rhenium, respectively.
Explanation: Physicist Henry Moseley discovered the atomic number of each element using x-rays, which led to more accurate organization of the periodic table. We will cover his life and discovery of the relationship between atomic number and x-ray frequency, known as Moseley's Law.
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Answer:
Volume = mass/density
Rearrange the equation for Mass:
Mass = Volume x Density
That is one way you can do it
Conceptually, just look at the units, the wood block's density is 0.6<u>g/cm^3</u> while the volume is 2.2 <u>cm^3</u>
So if density is every gram per centimeter cubed, and the volume is at centimeter cubed, the logical thing to do would be to multiply the density by the volume to get the total mass.
0.6g/cm^3 x 2.2cm^3 = 1.32g
<u>Therefore the mass of the block of wood is 1.32g </u>
Answer:
Explanation:
The equation is given as:
CH3CHOHC2H4CHO + CH3OH --> CYCLIC ACETAL + H2O
This above equation is carried out in the presence of a strong acid. There are five mechanisms employed and they are:
Step 1:
Initial formation of the hemiacetal which takes several steps
Step 2:
Addition of a proton. The hemicetal is protonated on the hydroxyl group (-OH group)
Step 3:
As seen a bond is broken to give the H2O molecule and a resonance stabilized cation.
The carbonyl group on the cation is enriched with the oxygen-18 got from the H2O molecule as seen in the mechanism.
Step 4:
An attraction occurs between electrophile and nucleophile i.e the stabilised cation and the lone paids of the methanol.
Step 5:
Finally, a proton (+) is removed from the molecule by a lone pair of electron on the methanol.
Attached are the Steps 1 - 5 mechanism below
Answer:
the final volume of the gas is
= 1311.5 mL
Explanation:
Given that:
a sample gas has an initial volume of 61.5 mL
The workdone = 130.1 J
Pressure = 783 torr
The objective is to determine the final volume of the gas.
Since the process does 130.1 J of work on its surroundings at a constant pressure of 783 Torr. Then, the pressure is external.
Converting the external pressure to atm ; we have
External Pressure
:


The workdone W =
V
The change in volume ΔV= 
ΔV = 
ΔV = 
ΔV = 1.25 L
ΔV = 1250 mL
Recall that the initial volume = 61.5 mL
The change in volume V is 

multiply through by (-), we have:

= 1250 mL + 61.5 mL
= 1311.5 mL
∴ the final volume of the gas is
= 1311.5 mL