I guess you can achieve this by changing the scale for the x axis. Here's a reproducible example and a possible solution.
# packages
require(plyr)
require(ggplot2)
# generate data
set.seed(123)
df <- data.frame(labels=LETTERS[1:6],
group=rep(1:3, each=2),
srednia=runif(6))
# limits for x axis
mylims <- head(unlist(dlply(df, .(group), function(x) c(levels(factor(x$labels)), "space"))), -1)
# additional space between groups
ggplot(df, aes(x = factor(labels), y = srednia, dodge=factor(group))) +
geom_bar(aes(fill=factor(group)),stat="identity") +
scale_x_discrete(limits=mylims, breaks=levels(factor(df$labels)))
# removing space within group
ggplot(df, aes(x = factor(labels), y = srednia, dodge=factor(group))) +
geom_bar(aes(fill=factor(group)),stat="identity", width=1) +
scale_x_discrete(limits=mylims, breaks=levels(factor(df$labels)))